Think practically. What is the tolerance between airspeed indicators? In my type it is around 6 knots. If the ASIs can be 6 knots out, what does it matter if you have rounded a decimal place up or down? Having said that, if you always round in the conservative direction then any compounding errors will also be in a conservative direction. A "conservative direction" isn't always the same though. You might have a V1 that is limited on the low side by VMCG so rounding it down is not the conservative thing to do, but the same V1 might also be limited on the high side by the length of runway remaining in which case rounding up isn't conservative either. In this case I come back to my first point, a knot each way isn't going to matter.