Well, how close do you need the value to be to 0? If you go through a lot of floating point operations which in “infinite precision” might result in 0, you could end up with a result “very close” to 0.
Typically in this situation you want to provide some sort of epsilon, and check that the result is just within that epsilon:
if (Math.Abs(something) < 0.001)
The epsilon you should use is application-specific – it depends on what you’re doing.
Of course, if the result should be exactly zero, then a simple equality check is fine.