TurboTax does not always use the Tax Tables. There are several ways that the tax may have to be calculated, depending on the items in your return.
One of the most common reasons for this is if you have any qualified dividends or capital gains. In that case, TurboTax has to use the "Qualified Dividends and Capital Gain Tax Worksheet" to figure the tax. That would provide you a lower tax amount since qualified dividends and capital gains have a more favorable tax treatment.
You appear to be using the Home and Business Edition, which is a desktop product--at least that is what is shown by your screen name above. So you can go into Forms Mode and see if your tax was calculated on the Qualified Dividends and Capital Gains Tax Worksheet or another method.
If you DID have qualified dividends and/or capital gains, then in Forms Mode look in the left column list for a form "Qual Div/Cap Gn", and you can click to view it.
There are additional ways that TurboTax may calculate the tax. Here's how to see what method TurboTax used in your case:
While you are still in Forms Mode, click to view the actual Form 1040. Scroll to Line 43. Just below Line 43, you will see a box called
"Tax Smart Worksheet" with several tax computation methods listed. There will be a checkmark that shows what method TurboTax used to calculate your tax.
See this screen image:
