A brief look at the story of the yen.
There were originally 100 sen to the yen and 10 rin to the sen but by 1953, given hyperinflation, a rather large war, and the impact of the gold standard, the sen and the rin were abolished and the yen, no longer 1:1, was fixed at 360 to the dollar.
He writes that the coin is called yen in English instead of the actual pronunciation en because of a spelling error. Not necessarily true. It was labeled yen due to the Japanese spelling ゑん, the first character historically being pronounced ye. The pronunciation of ゑ shifted to e around the middle of the 18th century, but the old spelling was retained for some time.
At any rate, the rest of the post is a good read.