
Depends on the nature of the "rounding."  X allows the user to do bit
arithmetic on pixel values, (i.e.,  XOR foreground and backgroun pixel
values together to calculate a foreground color that when used with a
function of GXxor fill change foreground to background and vice-versa).
If your rounding does not preserve these types of calculations then 
clients that use them will break.

	Ken