How is the zakat assessed for a clothing and accessories store when it is difficult to inventory its goods?

You must know the value of all the goods in the shop when zakat becomes due, because zakat is obligatory on the value of trade goods, not on their physical entities. Thus, upon the completion of the hawl (one lunar year), all goods prepared for sale are to be valued, and existing cash is to be added to it. Then, a quarter of a tenth (2.5%) of the total value is to be paid in cash.