Ok so that is not service charges that is taxes. You wont be able to toggle that. You should be using Calculation Type for service charge. You can use a Calculation Selector to put a button on payment screen that can toggle calculation.
Taxes are not meant to be used for Service Charges but Calculation Types are.
This is a long read but it should give you idea. Its not a tutorial but a discussion with someone wanting to do the same thing. Down near end he resolves it and with our help was able to implement it. It should give you idea.