Actually, they are not legal tender for debts greater than 25 cents. Neither are nickels. Dimes used to be, and may still be. It depends upon whether dimes are now considered "minor coinage." When these laws were passed dimes (and higher value coins) had silver content equivalent to their value (based upon a 1792 law which defined a dollar as 371.25 grains of fine silver and is STILL the legal definition of a dollar).
The bank did have the option to accept the payment in the form presented, but they were not legally obligated to do so.
ML/NJ
I don't know where you got that little nugget but United States Code, Title 31, Section 5103, says otherwise:
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. Foreign gold or silver coins are not legal tender for debts.
Take a camera to the nearest Federal Reserve Bank and see if they will swap the greenbacks for silver.
Interesting point. Where would you look to find the current law?