If you are looking for true multichannel integration, it is worth taking a look at the offering from Unipower (see http://www.unipowersolutions.com/). The EPOS and WebStore are just different views of the same software so all transactions are in a common database. The WebStore is just another store with its own branch ID so you can buy on line and return in store and all customer data is held across all channels. If a loyalty card or postcode lookup is used to identify customers in store, a customer will be able to see all their transactions irrespective of the purchase channel when looking at their account online. It will also be possible for store staff to look up the purchase history on a till or for the customer to view the history on a kiosk.
For retailers looking for a total solution, Unipower are now offering a Microsoft Dynamics Nav merchandising and accounts integrated system.
