Why is the income tax lower than expected?

I  m doing my federal income tax.  My taxable income after all deductions is $28,828.  Married filing jointly.

According to my hand calculation: Tax = $20550x10%+(28828-20550)x12%=$3048.36

 

I print out turbos tax return, it gives me $2,970.   Why tax from turbotax is NOT $3048.?

 

Is turbo tax wrong?  Help!