The rule I typically follow is to go one level of dress beyond whatever the typical dress for the company is. So if it is a startup where people would normally wear geeky black shirts with witty sayings on them, wear jeans and a polo shirt or a dress shirt, or even no-tie business casual at your discretion.

If the dress is normally no-tie business casual, wear business casual with a tie or a suit if that makes you feel comfortable. You definitely don't have to wear a suit for an engineering interview, you can wear a shirt and tie and no jacket.

So I would ask the HR person who scheduled your interview what people/the boss normally wear to work, then go one level higher in dressiness where one level higher is a fluid concept based on your personal comfort level.