Please note that the time accuracy is half a minute. So time from 0'00'' up to 0'14'' should be rounded to 00, from 0'15'' to 0'29'' - to "00 and a half" and so on. ;-) Of course nobody does that.
I've always wondered how does it look from the pilot's side, how do they check the clock. If they do anything to prove that their clock is at least remotely accurate, giving them a timecheck rouded to a full minute is in my opinion obsolete.