The extra 10% is on the original $59.99, so it saves you an extra $6 ($6.78 including the saved HST) on top of the original $10 saving. So a $59.99 game becomes $43.99.
Personally, $6.78 saved right off the top is better than $10 in credit that you have to wait 30 days for, and is ONLY good in the physical store. On top of that, in my experience, they almost never apply it properly, and you end up having to email them after 30 days to get it applied. That's too many hoops to jump through for me just to save less than $4.