This weekend’s sales tax holiday has been sold as a tax break for hard-working families but the biggest winners are retailers.

The holiday, which started 10 years ago, has grown into an event akin to Christmas sales for stores, and many hold extended hours and special promotions during the weekend.

Here’s what you need to know before you shop.

The Hours

The holiday started at 12:01 a.m. Friday and ends at 11:59 p.m. Sunday. Some malls, including Crabtree Valley in Raleigh and Carolina Premium Outlet in Smithfield, are opening at 9 a.m., an hour earlier than usual on Friday and Saturday. Some mall department stores are extending their hours even longer.

What’s covered

A variety of items – some of which you might not associate with back-to-school – are free from the sales tax. Here is sampling:

• Clothing and footwear of $100 or less per item.

• School instructional materials (reference books, textbooks, globes) of $300 or less per item

• School supplies (binders, chalk, book bags, calculators, crayons, highlighters, etc.) of $100 or less per item

• Sports or recreational equipment with a sales price of $50 or less per item

• Computer supplies (handheld electronic schedulers, printers, printer paper and ink, etc) of $250 or less per item

• Computers, including tablet computers and netbooks, of $3,500 or less per item. The state defines computer as CPU, monitor, keyboard, mouse and speakers when sold all together. The separate sale of a monitor, keyboard, mouse or speakers is subject to tax.

What’s not covered

Jewelry, cosmetics, protective equipment, wallets, eReaders and furniture – though it should be noted that some businesses in the past have made such items “tax free” to consumers by paying the tax themselves.

What you save

Tax savings will vary by county. Wake and Johnston counties levy a 2 percent sales tax on top of the state’s 4.75 percent sales tax. Durham and Orange counties levy a local sales tax of 2.25 percent. Buy a $1,000 computer and you’ll save about $70. Spend $688.62 – the amount the National Retail Federation says the average family spends on back to school – and you’ll save $46.48.

The deal with online sales

They count but you must send your order to a North Carolina address to get the tax savings.

If you get charged sales tax

Before you leave the store, make sure you got your tax break. If not, request a refund right then and there. The state cannot issue you a tax refund.