My natural response to these types of things is to try to figure how they work.
I wonder what their calculation methodology is?
1) Take customer order total...
2) Round up, take difference
3) Analyze product margins of supplemental offerings
4) Add product offerings where margins are less (<) than rounded amount. So if adding an Apple Pie costs .19 cents and the rounded-up figure is 52 cents, offer it!
So while the wheel is spinning, the computer is probably doing these calculations in about .00001 microseconds.
I might have to go into KFC and watch this in action.