When the U.S. first began minting our fabulous decimal currency, the lowest denomination—the half-penny—was worth a little more than today's dime. Anything less than a dime represents a value so low it wasn't worth dealing with in 1792, and it certainly isn't worth dealing with now. There are many big advantages in switching to a dimes-only coinage versus any other system:
-Dimes are an established coin in American society, and an extremely light coin, making a dimes-only system an easy plan to adopt, and easy to use.
-10 dimes to a dollar, not much is simpler than that. Any transaction would only require between 0 and 9 dimes, and only using a single coin makes counting a much simpler process.
-Rather than rounding to nickels like Australia, we can simply get rid of that pesky second decimal place. E.g. $9.5
There are a thousand arguments for other systems, and this is an arbitrary idea. But I would argue it's the cleanest arbitrary idea we've got. The dime is inefficient, and the dollar bill is inefficient, but these problems pale in comparison to the clusterfuck cause by the penny, the nickel, and everything else. The true primary hurdles would be solved by:
-Making dimes out of zinc, to appease the stupid zinc lobby.
-Putting Lincoln on it.
Then, a hundred years from now, that god we trust in willing, we ditch the dime for the dollar coin.