Modern POS systems have a lot of functionality for different ones. However, there are several essential features that you need to use in a retail business.

Ability to sale different product
The POS system should allow selling your types of products. For example, if you sell cloth, you should be able to process the same item with different sizes. The POS should give you the ability of sale through scanning barcodes, to make the process of selling quick and straightforward. For grocery stores, you need to sell items by weight.

Stock management
Successful store owners carefully track the stock of their products. They know how much this or that item they have in stock now and when they need to order them to replenish stocks. A proper POS system should help to get this information in a glance. At best, POS will offer the ability to order products with low stock from a supplier in one click.
A quick and centralized ability to add a new product or change parameters of an existing one is also a handy feature.

Sales analytic
Proper analysis is the key to success in retail. It is essential to see your best and worst selling products in your store. If you replace the worst-selling items with new ones, you can find things that increase your sales.
If you run the store chain, POS analytic will help you to know the best performing store and expend the best practices of the leading store to other outlets of your chain.

Customer care
Customer Retention is one of the cornerstones of successful retail. Right POS helps you to care for your customers, allowing loyalty program, having the ability of discounts and sending them digital receipts. It would help if you had customers list with the number of purchases to analyze customers and offer the best services.