Unlike what Edith has reported, real estate commissions are always NEGOTIABLE! There is no "norm" especially when comparing the Chicagoland area with Iowa City. Even within the same company, you may find different agents have different commissions. You should make phone calls to find out which agents provide the commission you are willing to pay and what they provide for that commission or choose your agent and negotiate the commission with that agent.
There are all kinds of variations on commission scales as well: fee for service (cafeteria style), discounted services, full service, assist to sell by yourself, etc. Research will help you discover which works best for you.
The figures Edith quoted do not apply to my market as we are very different as well. In like manner, buying a home in Chicago may cost a third more than in my market and two thirds more than in your market. Each market will charge what the sellers are willing to pay for competent professional help in marketing their home in this difficult time.
In our market (as I believe it is in most), the seller pays a full negotiated commission and a portion of that commission is given to the buyer's agent's company. As a result the individual agent does not get the full percentage you are paying for llisting your home. Essentially 4 parties are paid from the listing commission: the listing agent, the listing company, the buyer's agent, and the buyer's agent's company. If this system applies in your area, then when you shop as a buyer with an agent, you will not be paying a commission to your buyer's agent.
Good luck with your search.