Minutes to hours in decimal + round in C#

I'm trying to convert minutes to hours in decimal and round to the nearest fifteen minutes (rounded up).

Basically:

15 minutes = 0.25 hour

25 minutes = 0.5 hour

30 minutes = 0.5 hour

50 minutes = 1 hour

60 minutes = 1 hour

I haven't found anything relevant here on stackoverflow but another website tells me to:

var hours =  Math.Round((minutes * 100 ) / 60.0);

Which doesn't come near to the result.

I know I can't use Math.Round() (because it casts it to an int?). Same for TimeSpan (because it gives .TotalHours in a double).

What can a good approach be starting with dividing it by 60?