Having a margin account means the brokerage (Ameritrade) is willing to front you $$$. When it comes to clearing a penny trade (after you've sold), having a margin account means, technically, that Ameritrade will front you the funds from the trade even before they've cleared (which takes 3 days), so you'll have the $$$ available immediately to trade again. Just apply for a margin account.
One more thing. When you deposit funds into your margin account, that $$ is available immediately to trade most securities, but not pennies. It takes 5 days for the deposited funds to clear before you can trade pennies.
One more thing: If your account is an IRA, it can't be a margin account.