Bidirectional synchronize remote and local db for sales

Question

I sought and found a few dozen opinions about a similar problem, but none of that solves my problem. I'm writing an sales application that is used MySQL as a database to store information about the warehouse (articles) price and quantities, its changes (arrival of items and sold items). Information on the availability of items I would like to set up on a web server also, so that the database be (bi-directional) synchronized in order that site visitors, not only those in stores, also could purchase available items. Of course, the shop can sometimes lose their Internet connection and must continue to work off line, and after a connection has to be an option that differences among databases states are removed or leveled. Due that I gave up to put database on web and connect it from Windows application. Web server uses CentOS and MySQL. As a development tool using VB.Net and Visual FoxPro. Some idea, please? Thank you.