It is just like Orion said:
Here is a real live example of how banks work. In 2006 at Home Depot in Yuma we made a purchase of US $1642.42 in the AM and returned the defective goods in the PM, both on Master Card.
The resulting M/C statement showed a purchase of CDN $1903.68 (rate 1.159070) and a credit of CDN $1802.97 (rate 1.097753) on the same date.
So, the bank charged about 3.07 percent on each transaction but NO FEEs. :B
And yes I eventually received a refund but not without a few "up the ladder" phone calls.