Inventory what the SYSPRO tax connector and document services satisfy today, then choose between Microsoft localisations, Electronic Reporting and ISV products for each statutory obligation.
Localisation is the domain where a business owner's sign-off is not the sign-off that matters. A regulator's is, and regulators do not accept "the previous system did it this way" as an argument.
D365 approaches localisation through four layers, and confusing them causes most of the scoping errors in this domain.
The unit of work in this domain is the obligation, not the country and not the module. One row per thing the business is legally required to produce or calculate.
The translation task in the tax engine is a decomposition, and its shape depends on how the source determines tax.
Document services in the source becomes some combination of Electronic Reporting, print management and document routing in the target.
Three joins deserve naming, because they cross workstream boundaries and therefore go unowned.
The evidence supporting this module is thinner than for most others on this path, and the reason is worth stating plainly rather than papering over.
The obligation, not the country, is the unit of decision. Each filing, document and format gets its own disposition and its own owner. D365 determines tax from the intersection of a sales tax group and an item sales tax group. Flat source rate tables must be decomposed into those two dimensions.