There are buttons for adding/subtracting one dollar, a quarter, and a nickel. Or I can type it in the text field. In the list I can see what I need to top off, or look at the highlighted entry to pay the minimum that will get the 7% bonus and not have any spare change on the card.
I somehow missed the MTA App Quest contest but figured that one good push of coding I could add a data set which would qualify for the NYC Big Apps 3.0 Challenge. So in the end I chose the train color data from MTA.info Developer Resources to customize the highlight color.
One cute bit is that once you change the highlight color, the accent color around the buttons change as well.
You can get it at the Android Market: MTA Bonus Calc
