You can sell retail and wholesale at the same time if you get POS software designed for both B2B (business to business) and B2C (business to customer) sales.
Lightspeed Retail, Helcim, and Revel Systems are POS systems equipped with wholesale POS capabilities. They have features such as wholesale customer accounts, wholesale catalogs, bulk discounts, and wholesale-to-retail item inventory breakdowns so you can sell to individual customers and to businesses.