A customer can voluntarily give a tip to express gratitude.
In case of cash payments, the cashier will separate the tip from the rest of the cash (the amount that covers the invoice costs) and is not visible on the invoice or tracked in any way.
When paying by card a customer can pay gratuity in addition to the basic price. A gratuity of 5 to 20 percent of the price is customary when good service is provided. A customer can accept the calculated percentage or enter the amount on the keypad of the terminal.
Gratuity will be visible on the invoice.
Service charge is common for the service sector (e.g. restaurants). Service charge is optional and the customer can ask to modify the amount or to totally discard it.
If the service charge is already added to the purchase, gratuity will not be offered to the customer on the terminal.
Gratuities and service charges are tracked and visible on the invoice.
You may find them recorded in the invoice reports.
None of these charges are taxable.