Why am I losing over $500 when I put in my Roth 401k withdrawl information? It tells me my tax bill for that is only $157. That amount would be 10% of the original amount of the 401k.

The amount of withholding on the 401(k) is what is required to be withheld.  It's a minimum amount and should not be considered as the amount of tax that may be due on it.  Ten percent is the amount of penalty that might be assessed if the distribution is considered premature, before retirement age.

When the income is combined with your other income there will also be a personal income tax based on your total overall taxable income after exemptions, deductions and credits.  The combination of penalty and a higher personal income tax could likely increase your tax by the difference you see.