As per an explanation found here by Mac CPub fro Excel 2011 (for OS X) supposedly you can sort "Grand Total" columns as per the following: "... Excel for Mac doesn't have a "Sort by Grand Total" option, but you can select the grand total column and then use the Sort button on the ribbon to do this."
When I attempt perform this function it unfortunately seems to be disabled as you can see in this short screencast.
Any idea as to how to allow sorting by Grand Total?