Duty of music maker to carry article in case (5,3)
I believe the answer is:
sales tax
'duty' is the definition.
(thesaurus)
'music maker to carry article in case' is the wordplay.
'music maker' becomes 'sax' (a saxophone makes music).
'to carry' indicates putting letters inside.
'article' becomes 'a' (the indefinite article in English).
'in case' becomes 'lest' (as in 'lest we forget').
'a'+'lest'='alest'
'sax' placed around 'alest' is 'SALES-TAX'.
'of' is the link.
(Other definitions for sales tax that I've seen before include "sort of charge in the US" , "Levy on retail goods" .)