Rounding time

[Learning Excel]

A1 to A200 are starting time.
B1 to B200 are finishing time.
C1 to C200 formula is : =(B1-A1)*24*60 Copied down.
Giving me minutes difference between B and A.
When I have A1= 8A and B1=8:25a I get of course 25 minutes.
In order to do my work I need those 25 minutes rounded to 30, as
I only use 30, 60, 90, 120, 150...( half hour, one hour, hour and a half,
two hr...)
I think I need to change the whole formula but I have not clue about it, in
order to do the rounding time. Do I need a helper column or just different
formula?
Thanks for your help.

 

[Teethless mama]

=MROUND((B1-A1)*24*60,30)

 

[Learning Excel]

Got to give it to you Teethless mama, it works perfect.
Now I know, the more I know, the less I know.
I don't know.
THANKS !