SuitePOS for Salesforce can be purchased as a standalone solution.  This means you do not need to purchase Salesforce Sales or Service cloud (although it works with that as well).

All transaction integration to Salesforce is performed asynchronously and in real-time. This means that the POS terminal will not get tied up while the transaction is written, making things.

In addition, you can optionally provide access to the Salesforce1 mobile app.  This becomes very valuable when you need to search/explore your entire Salesforce instance directly from the POS.

The integration is deep and we utilize common Salesforce objects (such as Accounts & Products) where we can.  The written transactions can readily be ported to your ERP/Finance system of choice.