Remember that you will owe regular income tax PLUS the 10% penalty. The total tax could be between 10% and 36%, depending on your other income and tax situations. Don't forget you will also owe state income tax on the withdrawals (3-13%, depending on your state and income level).
The tax system is supposed to be pay-as-you-go, and you are supposed to have withholding or make quarterly estimated payments.
https://www.irs.gov/taxtopics/tc306
If you owe more than $1000 when you file your tax return, you can be assessed an underpayment penalty of 1-1.5% per month of the amount you were supposed to have paid.
