In 1857, Congress eliminated the half penny because it was worthless.
At the time the buying power of the half penny was more than a penny, a nickel, a dime, and two more pennies. 18 cents was the value when Congress said it was not worth making the coin anymore.
We could eliminate three of our coins without affecting the economy, but doing so would draw attention to inflation.
The dollar is metric, so we already have such a system. People often use kilodollars already, e.g. writing $2k instead of $2,000, but we could start using decadollars ($10) hectodollars ($100), too.