Seems like your report is candidate for a Subreport where the dataset is the result of your grouping and sum of the those values you need.

If not, add different grouping...

Try building a list (string) of categories and pass it to a T-SQL Function which will then parse each one by one. Call that function inside the SP that will return...

did you review this articule: http://support.microsoft.com/kb/326340