highly rec ConnectPOS, we are using it to sell handmade products, the POS system sync up all data with Shopify realtime so I can check the inventory and product status immediately, you can trial   

We currently use ConnectPOS for sync up all data. We need to migrate data from old system to sync up on Shopify, they directly integrate with Shopify and I import my orders to their POS system so that it sunc up realtime for me