The shopping holiday would be the opposite of a bank holiday. Banks, post offices & other businesses that normally close on holidays would stay open. Retail businesses, though, would close & give their employees a paid day off.
Retail workers rarely get to enjoy the holidays we give the rest of the country. This would give them a holiday in which they can still take part in many everyday activities (going to the bank, buying groceries, making appointments, even going out to eat), much in the same way an office work gets a day off but still gets to enjoy the everyday activities provided by the retail and service industry.*
This would also give the country a break from the holiday-as-shopping-day mentality.
*A similar, separate holiday should be given to the food service industry.