First create a calculated field similar to the following:
if (Sales)>0 then 'Sales' else 'No Sales' end
Choose the pie as the mark type. Place the above calculation on the color shelf. Then, place CNT(Sales) on the label shelf. Right click on it and select Quick Table Calculation-->Percent of Total. Right click again and select Compute Using-->the above calculation. Hold Ctrl and drag the calculation down to the angle shelf.
Hope this helps!
This worked wonderfully! Thank you very much!