I'd suggest this is more likely to be covered by the variable name an instance is stored in. You are right that x.round() is very unclear, but stepIterator.round() seems find to me.

I'm of two minds, as partially I'm trying to avoid function names that contain redundant information. stepIterator.roundToClosestStep would imply every public method on the class will likely carry the word "step" in them somewhere as well. E.g., isWalkableStep?