Tips or service charges are not usually added to a bill. In general, consumers tip a percentage of the amount of a bill to service providers such as to waiters, waitresses, barbers, hairdressers, and taxi drivers. The percentage and whether the tip is calculated on the amount of the bill before or after taxes depends on the practice of the particular consumer.
A tip or gratuity that is freely given by a customer, for example, cash not recorded on a bill, is not subject to the GST/HST. However, if you add a mandatory or a suggested amount to the customer's bill as a service charge, you have to charge GST/HST on that amount.