Google Play and AppStore as a third-party company can choose its own pricing and apply a tax which amount depends on what your state or region requires.
Taxes are determined by your local city/county/state based on your billing address. The tax is applied at the time of your billing based on the laws governing your area at that time. The amount may be subject to change as local tax requirements change.
Unfortunately, we are not able to influence the tax amount as it applies accordingly to the region you're in.