As , we know we are extending TAX class in order to have our own customization in place and then we use the below peice of code to show the Calculated TAX :
yourExtendedClass = new yourExtendedClass (buffer);
So now when you open the form , you will notice that Tab Adjustment is not available :
So what we need to do is , we have to override the method :
/// Returns a Boolean value that indicates whether the current transaction being calculated supports
/// sales tax adjustments.
/// true if the current transaction supports sales tax adjustment; otherwise, false.
/// By default, the current transaction does not supports sales tax adjustments.
public boolean useSalesTaxAdjustments()
this will make sure that we are having Adjustment tab on same form :