Like if an employee clocks in at 7:55 AM then goes to lunch at 12:00 PM, that 4 hours and 5 minutes.
Then they come back in from lunch at 1:00 PM and clock out from work at 4:38 (3 hours 38 minutes) All together that is a total of 7 hours and 43 minutes. (But why round to 7 hours 45 minutes) or even if the employee worked for 7 hours and 53 minutes why round to 8 hours?
Each business sets its own policy regarding time reporting.
Rounding to the nearest quarter-hour is just a way of trying to make doing math easier and less confusing, and also as a way of providing the benefit of doubt in case someone didn't clock-in for a minute or two.