Boston

[Alex]

I know that pennies are left at Franklin's grave too (I've always assumed it was inspired by the "penny earned is a penny saved" thing).

If there was a rational reason for it starting with Revere my guess is that it would do with the fact that Revere was, for decades, the dominant person in American copper production (though he is more popularly known for his silversmithing) and so pennies are a cheap connection.

But I'm just guessing without looking anything up. I imagine most people do it because there are already pennies there and people seem to like throwing coins at things even when there are 500 signs saying "please stop throwing pennies."