What are the penalties for cashing 401k between 55 and 60, if leaving the company?

If you left the employer where your 401(k) is located in the year you turn 55 or later, you can withdraw from that plan without penalty (you'll have to pay income tax on yor withdrawal, of course). But if you're talking about a plan with an employer that you left prior to age 55, you can not withdraw without penalty until the year you turn 59-1/2.; the early withdrawal penalty is 10% of the amount you withdraw.