You first need to understand inputs. The input command waits for the user to put in information and saves it to a variable. For example:
This should allow you to do the first part.
What you get from the user is saved as a string. But you want a number so you can do the tax math to it, so you first convert the variable into an integer with int() or a float with float(). Now the variable is a number you can do math with. This should allow you to do the second part the tax.
The final part is to continue the program or not. There are different ways to do this including using a while and variable, or an if statement and break. I'll quickly explain the while and variable.
If you put your entire code within a while loop, it will continue running until a certain condition is met. For example,
You ask the person if they want to continue. The person responds with a yes and no using inputs as shown above, and the answer is saved into a variable. If you then check this variable using an if statement, you can decide to keep running = True or to change it into False. Something like:
This should allow you to complete the third part of the question, which is to loop it until the user tells it to stop.
This assumes the user is friendly, and does not do any checks for if the user is inputting what you expect them to input