The law & case decisions of cash...
For your consideration I offer the below two cut & paste from the internet. Simple Google search. The statement that a merchant must accept cash is incorrect. I am also aware of this from a law suit brought by a classmate of mine from Northeastern University School of Law against the Commonwealth of Massachusetts Secretary of State, who had instituted a policy of non-acceptance of cash at his office. As a public entity, he was obligated to accept cash however if he was a private entity he could set his own policy. That was the Court's ruling.
Legal Tender Status:
I thought that United States currency was legal tender for all debts. Some businesses or governmental agencies say that they will only accept checks, money orders or credit cards as payment, and others will only accept currency notes in denominations of $20 or smaller. Isn't this illegal?
The pertinent portion of law that applies to your question is the Coinage Act of 1965, specifically Section 31 U.S.C. 5103, entitled "Legal tender," which states: "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."
This statute means that all United States money as identified above are a valid and legal offer of payment for debts when tendered to a creditor. There is, however, no Federal statute mandating that a private business, a person or an organization must accept currency or coins as for payment for goods and/or services. Private businesses are free to develop their own policies on whether or not to accept cash unless there is a State law which says otherwise. For example, a bus line may prohibit payment of fares in pennies or dollar bills. In addition, movie theaters, convenience stores and gas stations may refuse to accept large denomination currency (usually notes above $20) as a matter of policy.
From Wikipedia:
Legal tender is a medium of payment recognized by a legal system to be valid for meeting a financial obligation.[1] Each jurisdiction determines what is legal tender, but essentially it is anything which when offered ("tendered") in payment of a debt extinguishes the debt. There is no obligation on the creditor to accept the tendered payment, but the debt is nevertheless discharged. The creditor is not obligated to give change. Some jurisdictions allow contract law to overrule the status of legal tender, allowing for example merchants to specify that they will not accept cash payments.[2] Coins and banknotes are usually defined as legal tender in many countries, but personal cheques, credit cards, and similar non-cash methods of payment are usually not. Some jurisdictions may include a specific foreign currency as legal tender, at times as its exclusive legal tender or concurrently with its domestic currency. Some jurisdictions may forbid or restrict payment made by other than legal tender.[citation needed]
In some jurisdictions legal tender can be refused as payment if no debt exists prior to the time of payment (where the obligation to pay may arise at the same time as the offer of payment). For example, vending machines and transport staff do not have to accept the largest denomination of banknote. Shopkeepers may reject large banknotes: this is covered by the legal concept known as invitation to treat.[clarification needed]
The right, in many jurisdictions, of a trader to refuse to do business with any person means that a would-be purchaser may not force a purchase merely by presenting legal tender, as legal tender only must be accepted for debts already incurred.
Under U.S. federal law, cash in U.S. dollars is a valid and legal offer of payment for antecedent debts when tendered to a creditor. By contrast, federal statutes do not require a seller to accept federal currency or coins as payment for goods or services simultaneously exchanged. Therefore, private businesses may formulate their own policies on whether to accept cash unless state law requires otherwise.[3][4]