Originally Posted by 466SHH

It's a purchase of miles at one cent each. Not an award. So using your example, if you buy something for $1.01, you will earn 1 mile (as always) and they will place a $2.00 charge on your account, rather than $1.01. The 99 cent round up buys you 99 miles.

I guess the value in this depends on how badly you need AA miles. Might help if you are a tad bit short for a redemption, but not sure there's much point in buying these extra miles otherwise.