Are my tithes and offerings for church taxable?

Donations to your church are not "taxable". Was that a typo?  Did you mean to ask if they are "deductible?"

Donations to organizations such as churches, charities, etc. are deductible IF you are able to itemize deductions on Schedule A.  

TurboTax starts off giving people the standard deduction.  Once you have entered enough total deductions (allowed medical, taxes, interest, donations, 2% miscellaneous deduction such as job expenses, etc.), then TurboTax will switch over to itemized deductions.

In addition, medical expenses have an additional hurdle.  Only the amount of medical expenses over 10% of AGI will count (7.5% for age 65 and older.)

Have you entered all your various types of deductions to see if you can itemize?  

Your standard deduction can be seen here:
https://ttlc.intuit.com/questions/2568848-what-s-my-standard-deduction-for-2016