Can we set not to calculate tax for all requisitions (in US) and if needed to enable and then calcul

Dear Experts,
Can we set not to calculate tax for all requisitions (in US) and if needed to enable and then calculate ?

If we set the whole requisitions non taxable this should be fine right? And then the issue is how we need to enable if we need to tax a particular one. Can we check if the flag comes N and we can override to Y and it calculates then ?

Pl check and provide your feedback.

Thanks,
Romen