Rounding To Nearest 15 Minutes?

I have downloaded a punch in time clock from another user " Alex17", great job by the way. I was wondering on how to apply some certain rules this. I would need the times to round to the nearest quarter. Let's say someone punched in @8:01AM or any time up to 8:07AM, I would need it to round to 8:00AM, if they punched in from 8:08AM up to anytime to 8:14Am, I would need that to round to 8:15AM or if someone punched in @ 8:23AM it would round to 8:30AM....etc. I attached the form.

I need these rules to apply

7:00 - 7:07 round down to 7
7:08 - 7:15 round up to 7:15
7:16 - 7:22 round down to 7:15
7:23 - 7:30 round up to 7:30
7:31 - 7:37 round down to 7:30
7:38 - 7:45 round up to 7:45
7:46 - 7:52 round down to 7:45
7:53 - 8:00 round up to 8

or if this makes more sense

7:00 - 7:07 round down to 7
7:08 - 7:15 round up to 7.25
7:16 - 7:22 round down to 7.25
7:23 - 7:30 round up to 7.5
7:31 - 7:37 round down to 7.5
7:38 - 7:45 round up to 7.75
7:46 - 7:52 round down to 7.75
7:53 - 8:00 round up to 8