Finance isn't just banking and accounting. A huge amount of finance is modelling, simulations, signal generation, etc. where being fast is often way more import

Finance isn't just banking and accounting. A huge amount of finance is modelling, simulations, signal generation, etc. where being fast is often way more important than being completely 100% accurate. In financial modelling, errors from floating point are going to be insignificant compared to all the other assumptions you make in your models. I have worked in finance for my entire career, and everyone uses floating point arithmetic for dealing with money on the modelling side (sometimes $0.01 = 1.0, sometimes $1 = 1.0, depends on the institution/currency/convention/context, but we have to deal with fractional money anyway). They do NOT use it on the accounting/back office side. That would be a spectacularly bad idea. Those systems are designed for accuracy to the penny.