excel has three commands
ROUND
ROUNDUP
ROUNDDOWN
so to get cell b1 to display and round the contents of cell a1 would be
=ROUND(a1,1)
Would display contents of cell a1 rounded to one decimal place
or to round a sum would be
=ROUND(77/3,2)
would display 77/3 rounded to 2 decimal places
The number after the comma is the number of decimal places you want to round to, 0 being no decimal places.
ROUNDUP and ROUNDDOWN are used in the same way but will round in the direction stated.
Google excel round command for more help, though not sure how it will work with time, I hate dealing with time in excel :)