At POS we have developed a bridge between our EPoS system and a suitably coded eCommerce Website.
The integration to our own in-house web offering is very extensive and includes gift card data, loyalty data and promotions, including multi-buys.
However, if you have a well established website that you don't want to change we also have the ability to periodically export changes to certain data on the EPoS system. This exported data is then automatically sent via FTP to a configured website. Your web developers would simply code the website to react to these uploaded files and update your website accordingly.