Interesting discussion. (I am a lawyer and have served as a prosecutor, so I will probably botch this attempt to "clarify".. [insert lawyer joke here].
I think the key commercial points are the retail nature of the transaction and "notice of policy" . There's no "debt" if there is a simultaneous exchange of value. So if a person brings a can of beer to a cashier at convenience store, pennies tendered, the sale is easy to refuse and item can be reshelved. Restaurant, meal served and eaten, then tab presented and enough pennies tendered, customer is inconsiderate but not a thief.
Add a clear notice, "no cash, debit or credit only", or, more commonly, "no bills over $50", most problems are avoided, but
still the burden likely falls on the retailer to either accept the tender, waive payment, or refuse the transaction. (The boss of that cashier might have said "a cash-paying customer is always right".)
Such signs are very common in convenience stores to avoid conflict, and many small retail shops request payment before completing an un-restockable sale or service. Others take the risk out of tradition (restaurants) or two-way satisfaction aspects, such as barbershops.
In contrast, it is very clear that a true debt or tax can be paid in any combination of legal tender.
So, the pay-for-car-with-pennies is really more of a stunt. The dealer probably can refuse to hand over the keys if the contract allows. But, if the dealer delivered the
car on any portion of credit, it's probably time for a counting machine. (Of course, any savvy dealer would call the media, accept the coins with a big smile, and get free advertising.)
On the police aspects, it gets a
bit complicated. Larceny occurs when someone takes or keeps, but intentionally does not give. If a customer walked out with the product AND kept the un-accepted tender, then it is likely larceny in most US states. A customer can always walk away from a warm fresh
hamburger on the counter if the cashier does not accept payment of the full
price -- "sorry, I don't know how to count" --- everyone is unhappy but honest. If the customer walks out with a product after leaving the right amount of cash even in a "no-cash" store, I do not see a larceny, as there is no intent to wrongfully take possession,
nor, I
hope, any police interest. In many places, police will not arrest for "shoplifting" while the suspect is within the store , regardless of how the item was concealed, if the suspect is carrying enough
money to pay for the item. (Some of us may remember a former Miss America from the 50s who, among many travails, was arrested in the 80s for shoplifting, but only in the parking lot after the officers confirmed she didn't have enough
money.) There can be bias in enforcement policies in some places, sadly.