IBKR offers a discretionary order attribute which, if selected, allows you to place an order at an $0.01 increment between the market-specified $0.05 or $0.10 price increments. The order will then be submitted as Discretionary, using a Limit Price of the next lower (for buy orders) or higher (for sell orders) nickel or dime price level increment, and a Discretionary Amount of the distance between your specified Limit Price and the nickel or dime price.
For example, a discretionary order entered at a limit price of $2.43 would be rounded down to $2.40 with a discretionary amount of $0.03 for a buy order. Similarly, the order would be rounded up to $2.45 with a discretionary amount of $0.02 for a sell order.
The checkbox for this discretionary order attribute is located on the Orders page under the TWS Global Configuration menu. See website for additional details including disclosures regarding exchange fees and rebates associated with adding and removing liquidity:
For information on individual securities eligible for trading in penny increments, click here.