I hardly make it into the city these days, so not sure why I find these articles on saving money on NYC transportation so compelling.

Long story short, don't use the default amount on the MTA machines or you will be left with change. Instead, choose "Other" and input one of the following
($11.90, $19.05, $30.95) to end up with a zero balance.

EZPZ!

See Gawker article for more details.