Foreign currency charge being applied from home country

I have been testing the Marketpress plugin on my site by buying a $0.78 item from the store. The company I'm with is based in Canada and all the store settings for the plugin are set to Canadian funds. However, when I go through the payment process (with a Canadian credit card), a foreign currency charge of $1.09 is applied. If I'm buying from within Canada, with a Canadian card, and the store's base country is set to Canada, then why is there a foreign currency charge?