You always need to be able to account for every last cent on every account
Then that's your epsilon. Or, more reasonably, one or two powers of 10 further down. Absolutely nobody cares about a millionth of a cent. A few people care about a thousandth, though. Most people get antsy if you can't pin a calculation down to the nearest cent.
Floats are pretty much never fine for currency, but doubles are usually OK. There's a world of difference between a 24-bit mantissa and a 53-bit mantissa.
The problem is that some decimal amounts, e.g. 10 cent ($ 0.10) cannot be represented precisely using binary floating point. It doesn't matter how many bits you use since 0.1 have an infinite expansion in binary.
This is exactly what the article describes and explains. 10 cent plus 20 cent does not equal 30 cent, when using binary floating point. This is not acceptable in accounting, since at one point the error may accumulate and cause an error at the size of a cent (or more).
Then that's your epsilon. Or, more reasonably, one or two powers of 10 further down. Absolutely nobody cares about a millionth of a cent. A few people care about a thousandth, though. Most people get antsy if you can't pin a calculation down to the nearest cent.
Floats are pretty much never fine for currency, but doubles are usually OK. There's a world of difference between a 24-bit mantissa and a 53-bit mantissa.