From this month’s Imprimus, by John Steele Gordon:
Once the dollar was chosen, it would have been natural to adopt the British system of dividing the basic unit into twenty smaller units, and those into twelve still smaller units, the way American merchants kept their accounts. The Spanish system in use in the colonies—cutting dollars into halves, quarters, and eighths, called bits—would have been a natural idea as well. But Jefferson advocated making smaller units decimal fractions of the dollar, arguing that “in all cases where we are free to choose between easy and difficult modes of operation, it is most rational to choose the easy.”
That made Jefferson the first person in history to advocate a system of decimal coinage, and the United States the first country to adopt one. This was a very good idea, and, as good ideas always do, it quickly spread. Today every country on earth has a decimal currency system.
Contrast that with our (sluggish) adoption of the metric system!