switch in C# and all programming languages I am aware of require a constant label. You should not use it to test for > and <=, that's the job for if.
https://msdn.microsoft.com/en-us/library/06tc147t.aspx
... Each case label specifies a constant value ...
returnTotal should be an anonymous function not a public method; the method name should also be PascalCase.
Otherwise, there's nothing wrong with your program, nor anything interesting. For your record, a "real" business application doesn't code the program logic in Main. What you did was like just a HelloWorld learning exercise.
