Hey man, I know what you mean. HST sucks with its 12%. Living in Alberta is good with its 5% and it makes a huge difference when every one of your purchase is 7% less.
Don't look at it about HST or duties and such. Just think more about whether you are comfortable with buying jeans without trying them on. If you go and buy from TBS and save a couple of bucks but then you don't like the size and want to exchange them, it's going to cost you on the shipping. Other users have said that TBS isn't nearly as fast with the exchanges as they are with their deliveries. You buy from Dutil and you pay about $190 but you get to try and find your perfect pair (plus help support your local stores). Or you buy from TBS and it costs about $153 with shipping but they may not fit you as you want and have to exchange them, which may cost more. When I got my APCs from TBS, I got hit with about $26 for duties (with HST, you may be slightly more) so you may be paying up to $180 for them.
Just think if the $10 is worth it for jeans you are unsure about the size and maybe wait for Boxing Day for Dutil's sales (or hit up Holt Renfrew) and can actually try the jeans. Just don't go trying the jeans at Dutil and then buying online... That just seems a bit sleazy to me.