A friend of mine...yeah that's it a friend of mine....used to take the subway to the airport, then pay cabbies $10 for a few blank receipts and fill out the receipts for airport transportation. $5 for a subway fare paid, $30 for a taxi ride submitted.

And pretty much everyone my friend worked with did some version of this.

Virtually all taxis nowadays take credit cards. If this is a real issue for the OP, pay with a cc and you'll get a real receipt.