The US has a floating currency, as does the UK, Canada, Australia, Japan, and many others. This means that they can create money every time they spend.

If people jack up their prices and there isn't enough money being spent to support those higher prices, then they'll probably come back down. However, if there's enough money being spent in the economy to support the higher prices, then they stay high. That's inflation.

As the government spends, the amount of money in circulation increases. To avoid hyperinflation, they need to remove some of that money from circulation. This is accomplished by taxing people. Taxation is deemed preferable to hyperinflation.