Did you look through this thread? http://community.tableau.com/thread/135965
Basically, you can use Table Calculations to "hide" certain data, while keeping the data in the underlying data set--so totals can include all values in the data set, but you can hide to display the Top N, etc.
Best of luck. If you try and get stuck, I would always suggest posting a sample packaged workbook file when you ask a question on the forum--otherwise, tons of people will just skip right over it. Posting a packaged workbook is the best way to get help here on the forum, for sure.