Yes, There is a direct proportional relationship between the cost of items before tax and the cost of items after tax. 5.0 Step-by-step explanation: Given - A city has a 5% sales tax. To find - Is there a proportional relationship between the cost of items before tax and the cost of items after tax? Proof Yes, cost of items before tax is directly proportional to cost of items after tax. Reason With the increase in the sales tax, there is increase in the cost of items after tax, therefore, there is a direct relation between cost of items before tax and cost of items after tax.