Section 31 U.S.C. 5103
United States coins and currency (including Federal reserve notes and circulating notes of Federal reserve banks and national banks) are legal tender for all debts, public charges, taxes, and dues.
I find countless examples of people talking about making payments in pennies, only to have it refused. All of the articles I find state that these coins are "legal tender" but no company or individual is actually obliged to accept them. In fact, I have trouble telling whether pennies can be used for taxes or not. Questions like this abound.
What does "legal tender" entail? By that I mean, what is a transaction which either (a) would have failed normally but succeeded because the coin/currency was "legal tender" or (b) would have normally succeeded but failed because the coin/currency was "legal tender." or (c) court proceedings that would have gone one way, but went another because the coin/currency was "legal tender."
In other words, are there actually any circumstances where these magic words actually do anything to affect a transaction, or are they just words we put on our currency? I can find countless references explaining that parties do not have to accept some coins, but nothing offering a case where someone is actually obliged by this law.