Yes, practically I can see why. But when my W2 contains cents, and my tax forms make me sign for accuracy under penalty of whatever blah blah, seems pretty odd that they don't accept my cents and then do their own internal rounding. Maybe it was just the tax software I was using.
AGI is 40,001 to 40,025 then your tax is X dollars.
Being accurate to the penny isn't worth the trouble.