First of all, you should look at the problem from a different side and think why do you need rounding. I don't believe you really need it. It is very rarely needed. (One rare exclusion I known is generation of pseudo-random numbers; and I doubt that you are developing something like a new random number generator.
Much more likely that you simply want to show a rounded value on screen, and this is something very different
. In this case, you should think about formatting
, but not rounding itself. Please see:
By the way, even if you find a correct way to solve the problem using rounding, think again. It's much safer avoid doing it and focusing on formatting only. You don't want rounding to sneak into your calculations even by accident.