Metrics/durations/convexity/vega aren't monetary value, these are calculation values and I'm fine with them being whatever. If you're calculating averages to make decisions based on this I don't care if you're counting dolars or tomatoes.
Monetary value is $4.50 and it's representation of actual money passed through system. In practice this value is almost never undergoing any operations except for addition and subtraction. Any multiplication/divison etc. is left to specialized systems that return results wrapped in 800 pages of standarization documents, regulations and so on; systems where term "bit flip" is not a joke, but a risk.
As I wrote fintech != fintech, and I know many organizations aren't at that level of scrutiny, but a huge domain of people dealing with others' people money know that charging someone 1 cent too much is a tens of thousands of problems coming their way.