Adding the Sum of Total till the Month Shown in the Cross Tab Report in Crystal Reports 2008

I have developed a cross tab report in Crystal Reports 2008 which shows the item-wise sales data for every particular month grouped by the Division.

Which looks like this:

http://www.freeimagehosting.net/v2jj8

But now I want the Sum of The Total for that Particular month + Sum of Total for all previuos months.

For example: May-06 = Sum 0f May-06 + Apr-06 + Mar-o6 + Feb-06 + jan-06 + Dec-05 + Nov-05 and so on till the data exists. May-06 = 16012.50 + 21088.00 + 0 + 0 + 0 + .....