The way I would handle this would be to create a service item for 'comps' linked to a separate sales revenue type account.
Then I would use that item to create tax-free offsets to the sales items you give away - ie on a sales receipt you would sell 1 ticket for $100 + $7 tax then add a line with minus 1 comp at $100 no tax applied result is $7 net due from customer and all accounting completed properly