I'm looking at the ASX (Australian Stock Exchange), for the stock ARI, currently the last price was 0.158. However if I were to try to buy it at that price, Etrade Australia would give me an error about the price not matching the price step. For a share between the price of 10 to 49.5 cents, bids must be in steps of 0.5 cents, according to this. How have other parties traded at prices outside the permitted steps?
These orders at in-between steps have been executed through hidden orders. One such hidden order that may produce this outcome is a 'Centre Point order'.
You can read more about these and other hidden order in the ASX document titled New Order Types.