Or more specifically if the restaurant didn't take the pennies and sued you for non payment the court would rule that you had offered payment as the tender was legal. It doesn't mean the restaurant will be willing to serve you next time.
And every ecommerce site out there doesn't allow USD, but only a derivative currency convertible to USD on-demand with complex rules attached.
Never heard of this. Care to elaborate? Are you just talking about PayPal?
You actually can do that. It's only "legal tender for all debts", meaning that a restaurant would be required to accept the pennies after providing service, but my local bus line(that takes payment upfront) won't let you on if you try to give them pennies.
https://www.treasury.gov/resource-center/faqs/Currency/Pages...
And every ecommerce site out there doesn't allow USD, but only a derivative currency convertible to USD on-demand with complex rules attached.