How does turbotax guarantee it calculates the tax 100% accurate?

I am owing a huge tax bill this year, so I want to see if other software would figure out the same number.

When I did was I just entered figures of two W2s. Absolutely No credits or deductibles considered. Again, just two W2s. this was the simplest tax return case. Why did TT and TaxAct  show me more dues than the other three?

 

joint filing and each software summarized the same earnings on each W2. No typos entered.

 

TurboTax:   -$5,763

HR Block:  -$5,707

TaxAct:       -$5,763

FreeTaxUSA:  -$5,707

TaxSlayer:  -$5,707