The lowest US domination would be ten cents, the one dollar and five dollar bill would be replaced by coins. The $200 and $500 bills would be introduced.
Before anyone say that they dont want to be carrying around 30 $1 coins in their pocket, all I could say is don't carry that many in your pocket. The government is the only source that makes money, so you could either throw them away or give them to someone if you don't want them.
All states would then have to decide how to deal with taxes. The most sense would be is round up or down to the nearest ten cents. So 1,2,3 and 4 cents would be lowered down and 5,6,7,8, and 9 would be raised up.