The government must accept all legal tender to pay its bills and taxes. However, private entities may refuse to accept some legal tender as payment for a good or service. For example, a family could pay its student loan in pennies and the government would be required to accept them. However, a car dealership could legally refuse to accept rolls of pennies to purchase a new car. Stores may refuse $50 or $100 bills.
The European countries that converted to the euro as their currency declared the euro as its legal tender while discontinuing the use of its old currency as legal tender. For example, the German mark ceased to become legal tender on January 1, 2002, but the Bundesbank still permits people to convert marks to euros. A debit card is not legal tender because a merchant is not required to accept the card as a means of payment.