We are using Vertex and in this case there is a function module that does the access to the Vertex DB based on Country, Region, Zip code, City name to determine the jurisdiction code automatically.
I am not a 100% certain but I think the internal determination works like that, at least I saw it so for Canada
You define the structure. e.g. for Canada it is 2,2
which means 2 characters are used for the country, 2 characters the region
The entry in OBCP transaction would then be for Ontario: CAON
And it would be automatically determined based on the country CA and region ON in the address.