I know this isn't strictly a request for a dataset, but was hoping someone may be able to help.

I work with a company who has a few thousand shopfronts. We are looking for the best way to collect point of sale transaction data from as many as possible, and to send on a fairly frequent basis to a central location, so we can turn it into a data warehouse. 

Any ideas on the best way of collecting POS data as simply as possible?