If you are referring to the coordinate box, then this is only as accurate as your working units as set in your preferences. Try changing them to the nearest whole unit and see what happens. The coordinate box can and should be used for measuring a drawn element, but it should not be used for drawing/modeling those elements.
What I mean is that you shouldn't draw, say, a line and watch the coordinate box, wait for it to fall upon your desired length, and then click. You need to specify exact lengths as you draw. Do this by hitting the X,Y,R,A keys then typing the exact lengths and hitting enter. Then they will be exact, not just rounded to the accuracy of your closest working unit.
Cheers,
Link.