Hello 'metalbynumbers',
Most sellers list in US dollars. Yes, it's a bit annoying to Canadian buyers, particularly since our dollar is usually worth less comparatively, so the amount you pay in your own 'real' money is more than the listed amount.
Sellers list in US dollars because they want to sell internationally. They are aiming at the large American market who are happier to buy in their own currency. Generally, Canadians are a little more tolerant of foreign currencies, our buck having been measured up against the US dollar for ages.
Same for other countries, - they may prefer using their own, but 'American dollars' are an international language unto themselves, - readily understood everywhere. And sellers all over the world often list in US currency to attract that large (and ostensibly) wealthy market.
When you are contemplating a purchase, along with the item price and shipping fee, add a bit more. These days the difference will be about 4.5%, give or take, -- it changes every day. So if you like round numbers to add quickly in your head, use 5%. When the actual amount comes out slightly less, you'll feel good about it. 🙂
If you want to follow currencies, these two are among my favourites:
http://www.x-rates.com/calculator.html
http://ca.finance.yahoo.com/currencies/converter/#from=CAD;to=USD;amt=1
