How do I find out in app total purchases
How do I find out total costs of in app game
iPad, iOS 7
You can see your account's purchase history via your computer's iTunes : log into your account on your computer's iTunes via the Store > View Account menu option, you should then see a Purchase History section with a 'see all' link to the right of it. Click on that and you should then see a list of your purchases.
On your iPad you can only see a cut-down version of your history (the last 90 days) via http://reportaproblem.apple.com
For both you will need to total your in-app purchases yourself, it's not displayed.