1. Create a gift query for each appropriate gift subtype 
2. Run the report once for each query

OR

1. Create a new Gift Export in CSV format
2. On the General tab, include a query if necessary
3. On the Output tab, include Gift Subtype among the fields to export
4. Export the data to Excel and sort based on the Gift Subtype column (either ascending or descending)
5. Insert blank rows between the different gift subtypes
6. Add 'SUM' formulas in the blank rows to add up all of the gifts for each gift subtype