To expand a bit on what others have said:

If you're counting up, round down. If you're counting down, round up. A human expects the count to finish at precisely the moment we get to the last number in the sequence (zero, for counting down). Do a count in your head to see what I mean.

Apple chose a compromise by rounding to nearest, for it to "feel good", but you lose the ability to exactly predict when the timer ends as a human. Typical Apple.