Using letters to program the Sharp XE-A106?

You don't. The letters represent numbers that you gain by adding results in the table. There is a demonstration here:

http://the-checkout-tech.com/tubetorials.php

Copy and paste the link into your browser. When you see the list of tutorials, choose the one called PROGRAMMING PRINTING MODE.
It is from a different model, but it explains the use of tables.

Registerman
August 2010