Just wanted to report back - I created a new product for my customer called "Thank you for your service" and made it taxable, defaulting to $0.    I added it to a recently entered sales receipt that did not have any taxable line items, having first pulled a copy of the STLR.    Lo and behold, that invoice then appears in the gross and non-taxable amount columns in the STLR while the taxable and tax amounts remain unchanged. 

When I delete the product from that receipt, it again disappears from the STLR.

So, there's a possible solution that might work for some folks.

Plum