Put an additional text box in the details section of the report, Call it txtDetailsSum
set the control source for this to be the the name of the text box that contains the value of each line (=[txtLineCost])
Set the running sum in the data tab of the box to over group.
Preview the report, this text box should now be adding up the totals
After the details section add two extra box's
the first on is for the totals over the group, the second one is for the overall totals.
Test the control source for both as = [txtDetailsSum]
call one txtSumGroup and set the running sum in the data tab of the box to over group.
Preview the reoprt, you should now have two totals, on over each detal section and a running one over the group.
Create a new text box in the report footer and set its control source to = [txtSumGroup ]and set the running sum in the data tab of the box to over group.
Now set the visible property of all the extra box's to false.