In some countries, prices shown to buyers must equal the amount paid at time of payment. This means that all taxes (including VAT) must be included in the price (tax-inclusive pricing).
(e.g. Countries of the European Union...)
In other countries, there is no tax-inclusive pricing and the final cost differs, as the tax is different in every country/state. This is automatically handled by the Play Store / App Store.
(e.g. US, Canada, Australia...)
If you live in a country without tax-inclusive pricing, the respective added tax will be displayed before confirming the purchase.
Read more about tax rates and value-added tax (VAT) for Google Play: