Multiple sequential defaults to a field

[myme]

How do I set multiple sequential (or order I set) defaults to one field when adding new records. Example: When adding new customers to a form, there is a sales person ( out of 5) assigned to the record automatically and it needs to be in a order that can be set. Obviously I can set one sales person automatically when a new record (customer) is added, but I have not been able to set multiple defaults in an order I can set. Thanks