How much are taxes due on cashed in 401k?

If you are under 59 1/2, 10% will be withheld.

Even in cases of hardship, this money is best left where it is for retirement, particularly if you are young. It should be the last resort. If you leave it as it is, it will grow as the economy improves. Based on stocks, you would be taking a beating from selling at a low point plus the cost of the penalty.

See the related link to the IRS.