I remember reading an old "Book of Knowledge" that had a chart showing which coins were legal tender for what amounts. That is, pennies were only good for debts up to so much and dimes were good for this much, and to pay more than that you had to ise silver dollars or folding money. Of course the law has changed since then.
You used to see Silver Certificates (they were almost identical to dollars) that promised the bank would exchange them for an equivalent amount of silver. Not anymore, Jack! The law regarding those has changed, too. Of course, if you do find one, it's worth more to a collector than it's face value anyway.