Open Source Pos Software

It would also incude recipting stock, manage payments by credit card, multiple users, multiple outputs and multiple currencies?

PHP POS http://www.phppointofsale.com/ - merge with OSCommerce ( http://www.oscommerce.com/ ) to the end eCommerce feature full end.
JEA: http://jpos.org/

Do not use anything from sourceforge.net if it was not stable / mature tag. Remember, this is the lifeline of your business. Do not trust beta software.

Check out:

http://www.sourceforge.net

Sourceforge is the main repository for open source software. There is a search panel.

Good luck!