2c Internal Rev. Stamp On 1870 Receipt

Hi all.
Been without Internet since Tuesday's storm, so can't post pictures, but maybe someone can help.

Have an 1870 receipt with a perforated 2c Internal Rev. stamp on it (Scott 15c). Was wondering what the rule was regarding need for tax stamp on receipts and what the range was for the 2c to be the right amount.

(Receipt was for $24.12 for lodging, meals, and hydrotherapy services)

Pic to follow when I finally can connect laptop to the world.
Thanks in advance.
Chip

(Apparently, you can load an iPhone photo. Who knew?)

Tax on receipts was 2 cents . Didn't matter how much the receipt was for, as long as it was over $20, except for satisfaction of mortgage or court decree, or receipt for delivery of property. Rescinded 10/1/1870.

Thank you. Exactly what I didn't know before today.
Chip