A customer puts something worth ¥1,500 in their basket. Your payment code multiplies by 100 to get the amount in "cents", like it does for every other currency, and asks the payment provider to charge 150,000. The customer has just been asked for a hundred times the price.
The yen doesn't have cents. It has no minor unit at all. Code written with dollars, pounds and euros in mind assumes every currency splits into a hundred smaller pieces, and that assumption is one of many that money breaks.
Money is where localisation mistakes cost real money, sometimes yours and sometimes your customer's. This chapter covers storing it, showing it and charging it in a way that works outside your own country.