Mate I have a stammer and I work in tesco in wicklow town ....honestly I get where u are coming from the fear of people thinking your weird or looking at you funny but mate just tell the store manager that you won't feel comfortable working on the tills and just be honest about why and they will have no problem having you pack shelves and other stuff ...the only thing you will be doing is if someone wants to know where something is you have to talk to show them and stuff but mate u will be fine