I'm not totally clear on how your data is put together...is it possible to post a packaged workbook with some sample data?
Based on what I understand, each Rating Tariff has an associated Activation Date, and there would be some sort of Sales Date as well. Given that, I might set up a calculated field like:
SUM(IF [Activation Date]+30>= [Sales Date] THEN [Sales] END)
Then you could create 60 and 90 day calculations as well. Alternatively, you could set up one calculation and then have the 30/60/90 be filled in by a parameter.