$39.95
I need to remember that $39.95 is (one of) the magic number(s) when purchasing New York City MTA Pay-Per-Ride MetroCards with the current fare pricing.
Remembering that with the 7% discount given with purchases of more than $10 and the limit of only being able to make purchases in $.05 increments, a $39.95 purchase gives a $2.80 bonus so you’ll be able to get exactly 19 rides at the regular fare rate of $2.25 per ride from the $42.75 you’ll end up with on the card, leaving no money left over at the end.
There’s also other numbers that work: $35.75 gives 17, $37.75 gives 18, $73.60 gives 35, $75.70 gives 36, and $77.80 gives 37 rides; but I think $39.95 will be the easiest to remember.