OpenCart has many features that can be used to manage your store as a B2B application.
Define different customers groups such as default, retail or wholesale and set different prices for each group.
Logged In Display Prices
Set your store to display prices to only logged in customers.
Set price breaks depending on the quantity of being ordered by the customer. You can set the quantity discount to work with the customer groups so you can set different quantity discounts for each group.