I think you'll have to put an "ORDER BY tblCustomers.cuID" at the end of the query - DISTINCT probably requires the elements it's distincting on to be adjacent in the result set.
This means the result set will be in the wrong order, but you should be able to save this as a view, then query the view and use that query to put things in the right order. Assuming Access can handle this level of SQL. Failing that, use your application to put it in the right order, or move to a real SQL database.