The add total option can be used to display the sum of numeric values for tablix group or over all tablix data region.
Add Total option in the menu.


If the cell in body area is common for row and column group as shown in below snap, the Row and Column option will be listed in Add Total menu

Add Total option in the menu.

Before or After option in the cell to add total after or before a group in the tablix data region.

Add Total option in the menu.

Before or After option in the cell to add total after or before a group in the tablix data region.
