takeshi.asano@Japan 1997-03-27

Using currency instance of NumberFormat, default fraction digits is 2
for Japanese locale. It should be zero.
Japanese smallest currency unit is 1 Yen.

In the past, smaller unit "Sen" (= 1/100 Yen) or smaller
one(s?) were used. In some context, such as for exchange rate,
name of those old units may be used to express fraction.
But it's not generic usage. By default, fraction digits should be zero.