Design test cases to cover all boundaries for this system

An online store is offering customers a special offer. A customer can get $50 cash back when he/she spend more than $270, and can get another $50 cash back when spend more than $540 Furthermore, the store offers a 10% discount for site members. (cash back is calculated after discount) Suppose we are to test a system which calculate the last price we pay. An input to the system contains two numbers, (X, Y). X is an Integer > 0 represents the total price. Y is a Boolean shows whether the customer a site member. Output Z is a float represents the money you pay. Design test cases to cover all boundaries for this system. Some invalid test cases must also be designed. Note: a test case should contain both input and expected output, i.e., ((X, Y), Z)