For example - I want to resize an image to a canvas size of A0 841x1189mm.
I go to Crop canvas or image resize and type the above units into the box and press ok.
If I go back into the crop or image resize again it will appear at something like 840.99x1188.06mm.
I have noticed the same thing on Illustrator once or twice on different occasions when trying to resize images & rectangles - I would type in a whole number and then when I clicked on the image later it would appear with a decimal place.
The Dpi was set to 300 pixels/inch. (and I was trying to enter the dimensions in mm)
So then I guess this is to do with the variance between inches and centimeters?
I've honestly never really noticed this issue before and I've always worked in pixels per inch and I've never seen anyone mention using pixels per cm - I wouldnt even know what the equivalent size would be?