Almost everything is taxable except for maybe food at the grocery store. Taxes are normally never included in the price (unless otherwise indicated). So, always make sure you add 7% for the TPS or GST which is the federal tax and 7.5% for the TVQ which is the provincial tax, to get the total price you'll end up paying.
Also, tips are never included so youll have to add that as well.
Tourists can get a tax refund for GST/TPS. Check out the website below for more details and for the form. So keep your receipts (minimum individual purchase of 50$, minimum of 200$ before taxes)
You can find a counter for GST Tax refund at the Eaton Centre downtown on Ste-Catherine street.
EVERY FLIGHT you take ..domestic OR international comming out of Montreal, you HAVE too pay the 15$ AIF. It's to make the airport nicer and stuff. The best way to do this is to use your credit card and pay at the green machines (with the AIF/FAA signs). If you do this you won't have to stay in line when crossing the security. IF YOU LIKE SAVING MONEY (and being annoying) you can tell them there is no way in hell you'll pay an extra tax after all the taxes paid in this country!! What will happen is that they will take you in a room and have you write why you won't pay..once you've writen a few lines of whack..they let you go free to your plane!!
About tax refunds in Quebec: GET TO AIRPORT EARLY! To get tax refunds, you need to pass by the custom bureau before (in Dorval, it's in the arrival floor to the right of the elevators) so that the custom officer can look at EVERY item and stamp the bill. If he doesn't see the item, he will still stamp them..but a stamp saying he hasn't seen the merchandise, hence not garenteeing your refund! :(