There are constants, marginal rates and limits. Furthermore there are questions about how to determine jurisdictions.
It's very not easy and some companies make bank fulfilling client tax obligations or licensing based on their domain experience.
A scanned Word document -> sales tax calculator sounds more like a death march and my first determination as an engineer would be to confirm if management has done the due diligence as to the buy vs. build cost.
Assuming "regulations" is actually functionally different and not just some sort of lookup table for a multiplication constant, then having been in a situation with only 10 rules, even such a simple example can easily have a difference on the order of 10x just from prior experience with organizing large amounts of lookups into code (+edge cases, +consistent interface, +etc) instead of into tabular data.