Anything anything involving money is complicated to a fractal degree. I worked on a system to populate data into an large (well-known international) retail site

Anything anything involving money is complicated to a fractal degree. I worked on a system to populate data into an large (well-known international) retail site's order database. Representing the simplest possible concept of "this order had no sales tax" took 18 rows across 4 tables. The complexity was due to similar things you point out - the system had to support combinatorically large numbers of cases and even the concept of "nothing" had to be encoded in dozens of different ways.