Compare numbers with difference vs. if()

Hey guys,

I have the following issue. I want to compare several numbers (always pairs). I used both the difference, as well as an if() formula to check it. The results are not similar though. Example:

3,665.2958619613400
3,665.2958619613500

If I take these two numbers and do A-B, the result is "-" (zero). If I do if(A=B;"match";"no"), I get a no, so they don't match.

Why is that, does anyone know?