Likewise IANAL and this jives with my understanding: legal tender simply means that it cannot be refused in payment of a debt, e.g., to pay for fuel already pumped, a meal already eaten, a service already rendered.

However, there is no obligation to take when paying ahead of time, e.g., when ordering at a takeout counter, or otherwise as part of the offer and acceptance process, which is how all over the counter retail sales are characterized for legal purposes.

The only restrictions are on denominations, e.g., a business is not obligated to accept more than X coins of type T, etc.