If you had two objects that are so far apart that the distance could not/never could be measured, would you call it infinity? Then suppose one of the objects were to move an extra unit away from the other so the distance became infinity + 1, but that isn't the same distance as 'infinity'...
The problem with rounding up is that 1/2 a koala is not 'a koala', which is what the question asked for, so shouldn't, in the case of koalas, you round down?
Although, I think it's safer to round up unless the question specifically asks for something like 'full/complete koalas'...