Local Dining at a restaurant using Groupon - how do you tip?

Since I've never used a Groupon before, I was wondering how people usually account for gratuities and tipping? To me, it makes the most sense to tip on the full amount but I've heard that half of patrons only tip on the amount left over.

So... do you tip on the full amount or tip on the balance in excess of your groupon?

 

You're supposed to tip on the full amount. I've only used groupon once but have bought other coupons. But the one time I used it, I tipped the full.

 

Yeah, I tip on the full amount. To tip on the balance seems chintzy to me.

 

Yes, definitely tip on the full amount. However, how is everyone tipping since HST has kicked in?
I used to do 15%...but with the HST I don't wanna do that all the time.

 

Haven't changed my tipping habits, my usual range is 10-15% depending on restaurant type.

Although I guess I get lazy sometimes and just tip the HST now, before I would try to make whole rounded numbers ($45.00).

 

I usually tip 10% to 15% on the BEFORE tax and BEFORE discount amount.....

 

Has anyone noticed that when you use these group buy passes at restaurants, the service is a lot worse? Some could take that as justification to NOT tip on the pre-discounted amount.