Yes, I have the inventory system that you are looking for, ready, tested and fully functioning, very simple to use, however it can still be customized, bellow are its function;
Reference to Client Using it on freelancer: https://www.freelancer.com/projects/php/Software-for-retail-store/
>>Business information
>>Employee/ staff information
>>customer information
>>Inventory Management
>>Purchase Invoice Management
>>Local Purchase Order Management (LPO)
>>Point of sale integration (POS)
>>Sales profit and loss analysis between dates
>>User Access restrictions
>>Reports generation and flexible record search methods
>>Simple user interface and easy to learn
>>Can still be customized according to user preference
>>Can be operated within LAN and Local WiFi