if you suppress values in the report, you will need to use either a formula or a running total. I use formulas, DBlank uses running totals. In the formula, you would add the values that are not suppressed and display them in the footer.
Typically, formulas for summing come in groups of three. 1 to reset usually in the group header, 1 to display usually in the group footer, and 1 to increment usually in the detail section.
HTH