Staff members asking customers to buy the goodies.. While we're only there to do our own shopping.. At a very low budget

I have a problem with staff members who asks for money from us.. There's one in particular who asks us to by her thing! I want to do my shopping in an environment where i dont have to worry about an extra cash just because someone is going to ask me to buy them cooldrink.. One of the cashier's told me that her name is Thuli..

Please assist with this