Why don't do it as in added example instead?

The totals calculation doesn't depend on order the data are entered into tData Table. I.e. there is no need for entered data to be sorted in any way (e.g. by Group);
To add new groups later, you simply add a new row into tTotals Table with new group value, and after that you can add any number entries for new group into tData Table - without any need to redesign of any formulas.

In tData Table, you can hide the Group column, in case you want this.
I freezed the rows until the header row of tData table, so this header and tTotals Table will be always visible.

(Btw. You can define the Group column of tTotals Table as Named Range, and use it as the source of Data Validation List for Group column in tData Table)

Attached Files

SumExample.xlsx (12.2 KB, 4 views)

Thank you Arvil. Yours is another idea and approach that I could use later.