Hi Ben,
Yes, you can do the following:
TableDescriptor td = groupingGrid.TableDescriptor;
td.ChildGroupOptions.ShowCaptionSummaryCells = true;
td.ChildGroupOptions.CaptionSummaryRow = "Totals";
Whereas "Totals" is a summary row.
See the attached example.
ShowCaptionSummaryCells_6686.zip
Let me know if you need more details.
Thanks,
Stefan