For the first one - Let's think about this linearly. Periodically, the company is going to accrue for taxes; DR Tax Expense CR Taxes Payable. Then an estimated tax payment is due. So, you credit cash for the payment and then you.....
As for the second, at the end of the year you will not yet know the final "actual tax due." Look at the dates for the filing of the returns to see why this is so.