To reiterate what Eli said, an AON order is considered a special order and has less priority than a limit order. If you really want something risk getting a partial fill. Here is Fidelity's explanation:
What are the characteristics of an AON order?
All or none orders are allowed for most equity securities, and are allowed for thinly traded securities (securities for which there are few bids to buy or sell). Note that all or none orders are the lowest priority orders on the market floor because of the restrictions that they bear.
Placing an all or none condition on an order ensures that all shares in your order are executed at the same time. Without all or none, your shares may execute in more than one transaction (e.g., 400 of 1000 shares are executed as part of a partial order execution and, and the remaining 600 shares are executed later and possibly at a different price). https://scs.fidelity.com/webxpress/help/topics/learn_order_types_conditions.shtml
News 
Market Data 
Discover 
