I tip 20% on the total before tax, rarely leave less than 15% and can't remember never leaving a tip.
I don't tip on fast food or anywhere that has a tip jar.
If you combine the taxes to calculate the tip, keep in mind that the GST has dropped 2 points so what used to be a 15% tip in Ontario would now be 13%. I think.
On the one hand I find it offensive when a restaurant calculates in the tip with the bill, on the other hand it's usually less than I would have left so I just pay it.