As a pool guy, that 3" tablet is a Tri-chlor [stabilized with cyanuric acid) puck meant to slowly erode and chlorinate the water. In the case you're presenting, it will make the car smell like a pool and that's the problem - when you can easily smell chlorine, there is too much chlorine. Chlorine is an oxidizer so just imagine what that the fumes will do to the interior of a car... Your call on that one but I'll just nope out. :D
The easiest and cheapest way to take a cigarette smell off your car is to just fart inside your car. Just make sure that your fart is super stinky, and have your windows up.