The interview is a critical step in the employment process. Professional credentials and experience are very important assets to bring to the interview. Too, deportment, appearance, enthusiasm and a professional demeanor are of vital importance. The interview is a screening process. A process of filtering information, on paper and by personal impressions made and received.
Many companies are casual in their culture.
Don't assume that it is a best practice to come to an interview in casual attire unless requested to do so. A sports jacket, slacks, shirt and tie is always a good choice for the guys. A dress, pant-suit or similarly appropriate clothing is a good choice for the ladies. Answer questions and give verbal responses in a direct, pleasant and concise manner. Don't over-state or embellish upon information in your responses.