In the rpd go with 2 columns 1 for Sales which goes to dimension and other one is for sum(sales) which is for Facts in Presentation
in the report use accordingly
Umm do you want the total sales in a row of your table? or a column or your table? dont understand well your requirement.
1. However, if you want a calculation in a row:
-Please edit your view and in the View you could and set up you "Aggregation Rule"
2. However, if you want a calculation TOTAL in a Colum:
Create a column in your criteria section, and apply this formula: "sum( YouMeasure by "Sales")
Hope this help.