You can deduct either sales tax or state and local income tax. TurboTax will automatically use whichever one is higher. It might be that, even with the two major purchases, your state and local income tax is more than your sales tax, so you are getting the deduction for state and local income tax. Increasing your sales tax won't change your refund unless the sales tax becomes higher than the state and local income tax.
Furthermore, the deduction for sales tax or state and local income tax is an itemized deduction. It will not change your refund unless your total itemized deductions are more than your standard deduction. If you have not yet entered all of your itemized deductions, your refund might change after you enter the rest of your itemized deductions, if they make the total itemized deductions more than your standard deduction.
Since you are using the CD/Download desktop TurboTax software you can look at Schedule A in forms mode to see your itemized deductions.
