Floating point is intrinsically inaccurate. You can't use it to handle money.
With floating point, the assumption (x*y)/y = x does simply not hold.
With floating point, the assumption (x*y)/y = x does simply not hold.
I agree as much as the next person that you shouldn't represent money with floating point numbers, but I disagree that cash register software written in Javascript must automatically be incorrect (or more so that similar software in a different language). And I don't even like Javascript.
I'd assume that division is implemented as multiplying with the reciprocal (because thats faster). If that's correct, then any division by 3 (or any other number that is not of the form 2^i) breaks your cash register.
Because 1/3 represented as a floating point number equals 0.33333333.. and so on but not indefinitely, 3 * 1/3 = 0.99999999.. - which would be equal to 1 if you were using real numbers. But you don't.