Question

Hi all, i am trying to value Municipal bonds, because of their tax free nature do we adjust the discounting factor for the tax rate applicable ?
i came across following formulae while searching online.
P (pre tax discounting factor)= 1/(1+Z)^t
d (after tax discounting factor)= P/(1-T(1-P))
where,
Z=> spot rate of zero coupon bond for respective tenor
T=> income tax rate
Is after tax discounting factor mentioned above appropriate to use ?
Thanks..