Identify a situation that would fit into this scenario and explain how you would organize this calculation to solve it without a calculator. Assume a 5% sales tax rate.

Scenario
You are in a store and want to ensure you have enough cash for an unplanned purchase. You need to be able to calculate the sales tax for your purchase without a calculator.

Identify a situation that would fit into this scenario and explain how you would organize this calculation to solve it without a calculator. Assume a 5% sales tax rate.