Many fine dining restaurants offer after-dinner mints, suggesting a pun on the word “mint”:
 
“Nowadays, an after-dinner mint is what you need to pay the restaurant check”
 
“The way my girl ate in that restaurant I surely needed an after-dinner mint…a Fort Knox mint” was cited in print in 1956. The joke has been credited to Dean Norton (in 1961), Harold Allen (in 1964), Ashley Cooper (in 1971), Shelby Friedman (in 1977), and MAD magazine (in the 2000s). 
 
 
4 May 1956, Salisbury (MD) Times, “Small Fry Diary,” pg. 6, col. 6:
FRIDAY: “The way my girl ate in that restaurant I surely needed an after-dinner mint…a Fort Knox mint.”
 
14 August 1959, Appleton (WI) Post-Crescent, pg. A4, col. 7:
Financial Fact
Changing Times
After eating a meal in a first-class restaurant these days, you need an after-dinner mint, such as the one in Philadelphia.
 
31 July 1961, Boston (MA) Traveler,  “Grist For The Gals” by Ed. O. Kay, pg. 15, col. 4:
Dean Norton said it: “After a hearty meal in a swanky restaurant you need an after-dinner mint to pay the bill.”
 
16 April 1964, Ludington (MI) Daily News, “Case’s Column,” pg. 4, col. 2:
Know what an after-dinner mint is? That’s what you need in a fancy restaurant when the check comes around.
 
20 May 1964, Anderson (IN) Herald, “Try and Stop Me” by Bennett Cerf, pg. 9, col. 4:
After eating a meal in a first-class restaurant nowadays, you need an after-dinner mint, such as the one in Philadelphia.—Harold Allen.

13 July 1971, Aberdeen (SD) American-News,  “Earl Wilson’s New York,” pg. 4, col. 5:
WISH I’D SAID THAT: “An after-dinner mint is what a man needs nowadays to pay the restaurant check.”—Ashley Cooper, Charleston (SC) News & Courier.
 
27 October 1977, Wall Street Journal, “PEPPER….and Salt‎”:
Candld Comment
An after dinner mint is the money we need to pay in most restaurants.—Shelby Friedman.
 
you’ve got to be kidding’s blog
One-Liners from MAD Magazine
by yougottobekidding on January 18, 2010.
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Nowadays, an after-dinner mint is what you need to pay the restaurant check.