How do I set my default screen to a certain tab?

To do this go to System management->Main settings, If you want the default to be the table screen then edit setting 15 and change this to 1.

To have the department list as the default, go to setting 30 and edit this to 1.

To have the normal EPOS screen with the products and receipt, make sure both setting 15 and 30 are set to 0.