If I'm not mistaken, Sage 100 runs on a SQL Server platform. Is that true in your case? If so, you should be able to connect directly to the database via the Tableau SQL Server connector. You'll need the name of the database as well (and port if it's not the standard 1433) and a username and password. Do you have all of those things?
Have you tried setting up an access database with your sage tables...
I've been trying to connect Tableau with Sage 100 for a while.
quick test, add the AR_Invoice_HistoryHeader & Detail file to an access file. trim the data tables to just the columns you need i.e. Invoice date, bill to name, extension amount etc.
then connect the access file to tableau.