GST-Compliant Secure POS System

I’m commissioning a ground-up build of a point-of-sale platform designed for an Australian retail shop that needs to stay fully GST compliant while remaining affordable to run. From day one the software must log staff in securely, encrypt all sensitive data, and back itself up automatically... (Budget: $250 - $750 AUD, Jobs: API Development, Database Management, eCommerce, HTML, PHP, Software Development, Web Development, Website Design)