I've worked on international trading systems for a Fortune 500 broker-dealer that handled prices as IEEE-754 doubles, even though all currencies involved were d

I've worked on international trading systems for a Fortune 500 broker-dealer that handled prices as IEEE-754 doubles, even though all currencies involved were decimalized. In the US, stock prices all have to be a multiple of $0.01, but in some markets, this minimum increment/decrement of a price ("tick size") is based on the price range, so lower priced stocks have finer-grained pricing. Determining if the customer was sending in a valid properly rounded price was a pain, as an upstream system had already parsed the price into a double and didn't pass our system the string representation.