What should I wear for an interview at HollyFrontier Corporation?

I wore a suit to my interview at HollyFrontier. Most positions at HollyFrontier dress casually. Different managers have different ideas about the effort someone expresses during an interview so I would suggest dressing well. I interviewed with Texas Instruments during my college years for a coop position. The department head with a chemical doctorate appeared disheavaled. I attended the interview in a suit and was hired. After becoming a friend of the department head who was only known as Barney and never addressed as doctor among the engineers, confided that he never considered anyone who interviewed who did not wear a suit. He said he knew how financially strapped a graduate student could be and it was not important the quality of fit of the suit, just the effort to present the best appearance possible.