Price show decrease after choosing “Price inclusice of Tax”

Hi! For some reason after selecting show price inclusive of tax all the price in the store displays a decrease?? For example if i enter a product that is $9.99. It will show to be $8.93 in the frontend? How can I fix this issue? product price was entered after the option is choosen as I know this option wont update previosuly entered prices (even though these old prices also displayed decrease after choosing this option!) Thanks in advance.