“A nickel ain’t worth a dime anymore” is a bit of monetary nonsense that has been credited to New York Yankee baseball great Yogi Berra since at least 1979. A nickel (five cents) is worth half of a dime (ten cents). The joke is on the slang sense of “not worth a dime” for “worthless.”

“A nickel ain’t worth a dime anymore” is used in many comments to financial articles, especially those about the declining value of the dollar.
 
     
Wikiquote: Yogi Berra
Lawrence Peter “Yogi” Berra (born 12 May 1925) is an American baseball player and manager.
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A nickel ain’t worth a dime anymore.
 
1 August 1979, Valley Independent (Monessen, PA), pg. 19, col. 2:
Yogi Berra:“A nickel ain’t worth a dime anymore.”
(From “The Book of Sports Quotes” by Bert Randolph Sugar—ed.)
 
Google News Archive
8 August 1983, Newberry (SC) Observer, “Sports Shorts,” pg. 6, col. 1:
Yogi Berra has long been considered the master of malaprops.
 
He is, after all, the guy who once said, “A nickel ain’t worth a dime anymore.”
   
30 October 1985, Orange County Register (CA), pg. E14, col. 1:
Who said, “A nickel ain’t worth a dime anymore…”?
(“Yogi Berra” is the answer given—ed.)
 
Investment U
A Guaranteed Investment Scheme?
By Dr. Steve Sjuggerud, Chairman, Investment U
Thursday, July 14, 2005: Issue #452
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They say “a nickel ain’t worth a dime anymore,” and it’s true. A nickel back in 1970 is actually worth 25 cents a quarter today.
 
Salon.com
Monday, Apr 23, 2007 6:05 AM 02:22:38 CST
The 2008 election, explained by Yogi Berra
Everything you need to know about the presidential race has already been predicted by baseball’s greatest sage.
By Rick Ridder and Walter Shapiro
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“A nickel ain’t worth a dime anymore.”
 
Presidential politics is caught up in a frenzy of inflation reminiscent of the Weimar Republic or, at least, the Carter administration. Six candidates corralled more than $10 million each in the first quarter of 2007, a fundraising feat that only Dean pulled off anytime in 2003. But as Dean learned to his regret, there is only a finite amount of money that can be spent in places like Iowa before you start antagonizing the voters you want to woo.