Comment by dragonwriter

> the US has thousands of independent sales tax authorities

The US does not have thousands of independent sales tax authorities; administrative subdivisions of states are not independent, or even sovereign in the sense that states (which are also not independent) are, and can be dictated to by the state they are in, if the state decide there is a need, such as an urgent common problem that requires a coordinated solution.

> It really is a "herding cats" problem.

It's not, though. It's a "convincing cats to find shelter when it rains" problem, that you are trying to make harder by inventing the nonexistent need to also gather them in a herd. They aren't in a herd with the penny as the smallest coin, and they don't need to be in a herd if that changes to a nickel.

> Even at the level of all 50 States, resolving these kinds of coordination problems typically takes several decades.

There is no need for a coordinated solution between all 50 states, just as there is no coordinated policy on sales tax now between all 50 states. All that is necessary is that there is a solution in every place where the current tax policy would be problematic without the penny. There is no need for the policy to be the same in every jurisdiction with sales tax, just as the status quo policy is not the same in every jurisdiction with a sales tax.