If your office has an increment set for hours rounding (as specified in the Settings screen of your Administration application), your "Round Entries" button will be enabled at the bottom of your timesheet:
When clicked (and after your confirmation), this button will round all hours displayed on your timesheet up to the nearest increment specified for your office rounding, which can be set as one of five, six, ten, fifteen or thirty minutes.
For example, if your office had set hours rounding to be the nearest fifteen minutes and your timesheet appeared as follows after a day of using your stopwatch timer:
Clicking the "Round Entries" button would prompt you for confirmation:
With a click of "Yes" on that message providing the following result:
As shown, all time entries are automatically rounded up on this timesheet to the nearest 15 minutes (0.25 of an hour). For example, in the timesheet above, 0.1 hours have been noted for GUI Design. On rounding, this figure is adjusted upwards to the minimum billing increment for this office of 0.25 hours.