99 Restaurant Lynnfield

I don't really frequent the 99 anymore but since it is National Cheeseburger Day today and the 99 is offering their burgers for $5 I decided to go back and went to the 99 Restaurant in Lynnfield. Last year I had a very pleasant burger at the 99 in Woburn. It turns out that NCD is actually on September 18..

They are conveniently located just off Rte 95 and have plenty of parking.

I was never offered any popcorn, so that was the first strike. I ordered the Sweet Heat Burger ($10.19). "This juicy burger is topped with cheddar cheese, sweet jalapeño relish, crispy jalapeños, lettuce, tomato and a chipotle drizzle". The bun was tasty and nicely toasted and the fries were, as usual, excellent and everything looked good. This was a good sized burger with a nice char and when the manager stopped by and asked how everything was, I cut into the burger and it was seriously well done. I had ordered it medium rare. The manager took it back to the kitchen for a refire and also took the burger off the bill. They get kudos for how this was handled.

This is the second try and again it was well done and I didn't wait for another (probably) well-done burger so I ate this one. It was loosely packed, completely devoid of seasoning, but was still somewhat juicy. The best part was the crispy jalapeños who didn't stay crispy for very long, sitting in the sweet relish with chipotle drizzle on top. When I was almost done, the manager showed up and I showed him the burger and suggested he should talk to the kitchen. He apologized profusely and gave me a chit for a free entree. Again they get kudos for great customer service.

One 99 looks much like every other 99 and they seemed to do a brisk lunch business.
Question: When food is heavily discounted, do you base the tip on the bill amount or the original price?