How to determine transaction cost:
Say for example that you want to trade a 1K lot of USD/CAD on a CAD denominated account. Simply add the commission to open and close a 1K USD/CAD trade (CAD$0.05 + CAD$0.05 = CAD$0.10) with the value of the spread (0.5 pips x .10) = $CAD0.05.