Make util method public

A utility method is private but we need it elsewhere. This CL
just makes it public. Also it restricts the use of the method to
just rounding positive values to positive multiples. It is only
meant for rounding time.

Test: robotests
Bug: 77874313
Change-Id: Ieb222c7f752b6a907fca5f91ddd4f4a4b67a0d2a