how do I show grand totals for subtotals

[rogbert]

I can get a Grand Total but would I would like is for the Grand Total to show
grand totals for the above Subtotals beneath it.

City 1 Total
Prod A subtotal
Prod B subtotal
City 2 Total
Prod A subtotal
Prod B subtotal
Grand Total
Prod A subtotal
Prod B subtotal