Make pennies into nickels

Mr. Velde, in a Chicago Fed Letter
issued in February, has come up with a solution that would abolish the
penny, solve the excess costs of making nickels, help the poor, keep
the Lincoln buffs happy and save hundreds of millions of dollars for
taxpayers.

As Mr. Velde explained in an interview, “We face a
very medieval problem so I took inspiration from the medieval practice
of rebasing.”

He would rebase the penny by having the government declare it to be worth 5 cents.

We would then stop coining nickels at a loss.  Here is more, from Austan Goolsbee.  I am reminded of Neil Wallace’s work from the 1980s on the indeterminacy of equilibrium exchange rates in the absence of legal restrictions.  If we take away government acceptance at par for taxes and the like, is there not an equilibrium where each penny is worth a million dollars?  More ambitiously, if the U.S. government declared that each $20 bill is now worth $100, or each $100 worth $500, would the real exchange rate adjust immediately?