If you cannot get the calculator to work, the rate might be set to 0%.
The screen displays the original retail price before tax. how to set tax rate in casio calculator
This can happen if you didn't press the TAX+ key (for SET models) or if you exited the setup mode too quickly. Try holding the % key a little longer (at least 2 seconds) until a clear indicator appears on the screen. If you cannot get the calculator to work,
: Press the [TAX+] key to tell the microprocessor you are modifying the tax variable. how to set tax rate in casio calculator