> I have never in my life joined a software project for any organisation that was able to do basic arithmetic on money correct
This observation should tell you that's it actually quite viable to be off as long as the errors are small enough.
This observation should tell you that's it actually quite viable to be off as long as the errors are small enough.
The size of the errors almost always is a large factor in their decision, but ultimately the software we write exists to serve the needs of the business, and if the business decides that larger errors are okay for some reason, then so be it.
Sometimes there's also value in doing something objectively poorly, but in a predictable and well-understood way.
Unilaterally starting to "do numbers better" sounds like a recipe for, let's say, interesting times in the finance/accounting world.
But if I imagine myself as a business owner I would be annoyed with my accounting firm if they spent billable hours chasing down a discrepancy of a few pennies.
As long as things are consistent, no one cares if you are correct. If you lose a penny in the backend calculation, and the frontend shows the amount without the penny, and the email contains the amount without the penny, and the PDF download contains the amount without the penny, no one will care that there should be a penny there.
It becomes problematic if some places are wrong and some are right, and they are not consistent. You won't get credit for being right in only some places.
As long as the error is small enough to be inconsequential, being consistent is more important than being correct.