Do we need a point of sale system in our retail store?

BVS would highly recommend it.

Without one, you lose the ability to capture exactly what you've sold during the day.

Without knowing exactly what you've sold during the day, you lose the ability to determine how many units you have in stock.

Without knowing how many units you have in stock, you lose the ability to forecast your inventory requirements.

Without the ability to forecast your inventory requirements, you'll be out of stock on many items.

Without the ability to know what you're out of stock on, you are letting disappointed customers walk out of the door with nothing.

Have too many disappointed customers, and you'll lose the ability to pay your bills.

Lose the ability to pay your bills, and you'll lose your business.

That being said, it's really up to you whether you wish to invest in a POS system, but you really do need a data capture device at the point of sale. If you are to manage inventory properly. Without one, you're flying in the dark (and most likely into the side of a mountain).

Personally, BVS would make the investment, for the aforementioned reasons.