Need more than one row in my gridview footer

I have a gridview control on my web page with a list of items on a sales order.  I multiply the quantity times the unit price to get the extended amount.  This works fine presently.  I also added a footer to my gridview where I total up all the extended amounts and display this as "Product Total".  This works great too.
Now I want to add a Tax Total right below the Product Total.  And then a Grand Total right under the tax Total.  So I would now have 3 rows in my footer Like:
Product Total:   $1000.00
Tax Total:             $50.00
Grand Total:     $1050.00
Not sure how to add more than one row to my footer.  Here is my code:
<asp:TemplateField HeaderText="Unit Price" SortExpression="UnitPrice" HeaderStyle-HorizontalAlign="Right" ItemStyle-HorizontalAlign="Right& ...