Here is how you can save up to 3.5% on a round trip flight in Canada, off any fare.  If you're from Alberta you might as well stop reading now because you can't save anything!

In Canada the sales tax rates differ from province to province.  The highest taxes are paid in Quebec (about 12%) and the lowest in Alberta (7%).  I happen to live in Quebec and needed to fly to Alberta.  A round trip ticket on a seat sale carried about $50 in Quebec sales tax.  I was able to save half of it, or $25, by booking in two segments: A one way trip to Alberta, then another one-way returning.

Total base price was the same, but the provincial sales tax was cut in half because I essentially bought the return trip from Alberta.  It makes sense:  The service is delivered from Alberta so I should pay Alberta tax.  I wish Air Canada did this for me automatically, but I guess then an Albertan visiting my province would have to pay more too.