Go to the Account section located in black top bar of the page and click on it. (Make sure you are signed in). Then on your Purchase History there is a list of all your purchases, you can add up your total. If you did all your shopping online, you can use the order history. Click on the order number and it comes up with the total for that order. If you are calculating for VIB or points, make sure you subtract your returns.
Hope this helps!