Why is the result of RoundTo(87.285, -2) => 87.28

Question

I expected that the result would be 87.29. I also tried SimpleRoundTo, but produces the same result.

In the help there is also a \"strange\" example: ms-help://embar

Answer 1

87.285 is not exactly representable and the nearest double is slightly smaller.

The classic reference on floating point is What Every Computer Scientist Should Know About Floating- Point Arithmetic.

For currency based calculations, if indeed this is, you should use a base 10 number type rather than base 2 floating point. In Delphi that means Currency.