> Thats why when people drop a pile of pennies on the counter, the clerk doesn't tell them to go to hell.

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.