Sum of filtered group in SSRS
You could try setting the filter on your tablix instead of the group - any sums in the tablix are then subject to that filter.
There are many ways to address this. I would probable move the filter up the data stream, either into the query, or into the Dataset properties.
But some two other methods are described in this MSDN Community thread:Either creating a fake total row within the group members that contains the =RunningValue(...) function, and set the visibility to only show on the last row; or refer to another page item where you can get just the total of your filtered items.