For simple one-store systems, I suggest that you have it customized by a competent freelancer. Most IT companies charge as high as P50,000 for simple systems but freelancers charge between P5,000 to P15,000 only for simple systems. You will need to purchase a decent POS terminal that is preferably PC-based so that it is easy to integrate to Windows-based software such as MS Excel or MS Word.
Customized software is a good option because the programmer can work with you in designing and implementing the software instead of a generic software that you need to learn and react to.
I hope this helps.