Round Time?

Hi,

I'm worndering how to round time to the nearest 15 minutes or quarter when using this format: 0:00

For example, I have a calculated duration of 1:05 (1 hour & 5 minutes)

How would this be rounded to 1:00 (1 hour)?


Here's the current function I have:

=SUM(P29:P39)
With 0:00 format


Thanks