I am STILL struggling with this and I have version 26.5!
Please help me fix this problem ASAP.

I am using Illustrator version 25.4.1 and this issue STILL persists. It is really unfathomable to me how Adobe can allow such a foundational malfunction to continue for years. Thank god for Figma...

This is still happening in 26.0.3 for Mac with type objects UNLESS they are set to Area Type.

This bug also came back for me. Any fixes on the roadmap? This is really annoying, since I use Illustrator to create CNC drawings and need to be able to rely on exact measurements.

This bug came back in 25.2.3! Any work around or fixes?

7/8 = 0.875 but illustrator rounds it to 0.88. Very annoying!!!!

Making patterns and pattern brushes I depend on precise measure to avoid gaps and flickers in the print result. Meanwhile we are at Illustrator Version 25.2.3 (64bit) and my impression is that since the last update these issues got worse. Objects that have been placed with precise measures after deselecting and selecting again the transform menu shows values and coordinates with many digits behind the comma. Not to talk about the glitch (duplicate anchors etc.) to be found in high scale view after using simple pathfinder functions like substract back. After almost 30 years working with Adobe Products it's sad to see them getting more and more expensive and less helpful. I'm seriously thinking about a change.

24.3 and I am seeing tons of these problems still with what should be exact numbers, like 1000 x 1000 px becoming 999.9999 or 1000.0001 px. Same with mm, etc. For someone like me with OCD, this is causing serious headaches. It's a bit ridiculous actually.

Not fixed on OSX 10.15.6, Illustrator 24.3. Place an object at a specific point in a document by keying in a whole number in the Transform panel or the Control panel -- eg put item at x = 2p6, y = 18p6 -- it will move it to 2p6.0001 x 18p6. Snap to pixel is off. This problem with precision is not new; it only goes away for some updates.

It's a kind of sad funny, that a big company like adobe can't fix this truly. It feels like that they are working around the bug, instead of fixing the problem.
They should look at Blender. There is no calculation from one unit to the other internal causing such problems. You just give the units the common name of your local area like inches or centimeters or pixels and so on. Only in the moment when you export your work in other file-formats unit will be converted. A very easy and clean solution for such a problem.

Also, we are on 64-bit systems those days. With the old IEEE-754 (1989) float and double we can have significant digits between 6 and 17. So how can it be in the year 2020, that adobe does't find a way to make here software work correct and accurate on 3-5 significant digits?

Long-Time users like me, sometimes wish back to the time of CS2, when the problems were still bearable.

JMF basically summed up my exact thoughts on this issue. I'm keeping my fingers crossed in hopes of it being resolved in the next release.

I posted this on the community forum and it was recommended that I share it here as well. Following are my comments in full. Issue definitely not fixed in 24.2.1.
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I just upgraded to Illustrator 24.2.1 a few days ago and have had issues with my Keyboard Increment settings and Transform palette measurements ever since.
I've seen several others questions here and elsewhere regarding how Illustrator will round off artboard sizes (x.375 becomes x.38 etc) but this is quite the opposite problem.
I usually work in picas and, since the dawn of time, my Keyboard Increment setting in General preferences has been 0p1. Now it keeps defaulting to 0p0.9996. Ditto for the measurements that show up in my Transform palette. If I reposition something or make a size adjustment, either with arrow keys or specifically typing what I want, it changes my specs.
Say I have a box that is at 15p0 on the Y axis. If I nudge it down, it goes as follows: 15p > 15p0.9996 > 15p2.0004 > 15p3 > 15p3.9996 and so on.
I know that my end results are not going to be visibly different to the naked eye. But it's a problem for my general workflow. I gave a nice clear example with easy numbers but it's more disorienting when numbers are randomized and, for example, maybe I'm just trying to look at two items quickly and see if they're the same.
What happened with Illustrator? Is there a way to get back some "normal" settings? I'm a print designer and, even if I'm making dielines, my work is not critical to the ten-thousandth decimal.

This very clearly still isn't fixed on 24.2.1.

私も同様のバグにまだ困っています。
テキストの位置を数値で合わせようとしても勝手に変わります。
早めの対応をお願いします

I have 24.20 and am still having this issue. It doesn't matter what unit I'm working with (inches, mm, etc)

With the release of 24.2 the previous bugs, new document and corner radius decimals are fixed. Still having a issue with the move tool. See attachment

The issue hasn't been fixed in 24.2 release.
All vertical/horizontal lines including guides appear as 0.0001px/pt in width/height.

See also line width/height becomes "0.0001 px"
https://community.adobe.com/t5/illustrator/adobe-illustrator-cc-2020-24-1-3-version-quot-0-0001-px-quot-issue/m-p/11184931?page=1#M179955

I also found this problem recently. It seems that the problem is more serious in the legacy ""File New"" . It's too troublesome to have to be manually modified every time.

Round corners shows also decimal places
Create a rectangle 100X100 px
Round corners to the maximum. Value shows: 49,9999 px
Previous versions: 50 px