ADO might be more appropriate since you seem to need two way communications.
DAO/ADO
http://www.erlandsendata.no/english/index.php?t=envbadac
Since POS systems are written using code, and Excel provides a programming
language, you could certainly code a POS system in Excel to meet your
specific needs. Printing out a receipt should require little more than
filling in the information in cells in a worksheet formatted to appear as
you want to print it, then printing. If you want the data added to a
database, then you would need minimal code to do this.