Hello!
I am ready to help you with your task!
Does your client need a web-based or desktop POS system?
Any printers/code readers implied?
I already had alike experience - developing from scratch web-based CRMs for a travel agency and recruitment company using PHP+MySQL+jQuery+Bootstrap3+GoogleAPI.
- Bookings keeping
- bills and invoice making
- managers accounts managing
- Google Drive files upload
- Gmail messages fetching
- reports, contracts and etc docs generating and etc...
I can send you screenshots of the system, I guess it's similar to what you need
You can also take a look at my portfolio.
Please do not hesitate to contact me via messenger!