new System.TimeSpan ( 0 , 150 , 0 ).ToString()
System.DateTime d = System.DateTime.Parse ( "1/9/2012 1:30:12" ) ;
double minutes = d.TimeOfDay.TotalMinutes ;
This yields 90.2 -- what you do with the fractional part is up to you; Round, Ceiling, Floor, etc.
And if you want your SQL to add the seconds as partial minutes, you can change the second
-- you should then get 90.2 there are well.