I would create two sheets one for Sales and other for volume.
Then i will show one of them based on selection and hide another.
It is like sheet swapping based on parameter.
you can make 2 copies of KPI_ALl , something like this;
if parameter = Volume then volume measure
elseif parameter = Sales then null
if parameter = Volume then null
elseif parameter = Sales then Sales measure
set the default properties-Number format of each calculation for currency or no currency
put both calculations in the view.
when you change the parameter, one copy will be null showing nothing , and the other one will show with the correct format