http://cognosandme.blogspot.ca/2010/08/creating-overall-percentage-summary.html
User Query - Creating Overall Percentage Summary Values in Reports
This requirement is in response to a user query:
Requirement: Display Dates, Sales, Percentage Sales along with summary total.
Solution:
Step 1: Create a crosstab report with Year, Month, Sales data items.
Step 2: Create a data item Total Sales - total(...[Sales] for report).
Step 3: Set the Aggregate and Rollup Aggregate functions to calculated.
Step 4: Create a data item Percentage - [Sales] / [Total Sales] and set aggregate and rollup to calculated. Drag this query item into the crosstab.
Here are a couple of other ways to format the above information: