Sunglasses aren’t there just to make us look cool (although it’s debatable how cool you’ll look with the ones from dollar stores). They’re supposed to protect our eyes from harmful UVA and UVB radiation. It can damage our retina and cause many other issues.
Cheap sunglasses mostly don’t provide any protection. If you plan to wear them only occasionally and at hours when the solar radiation is low, then they might be alright.