Missouri retailers and parents are preparing for back-to-school season with the sales tax-free holiday weekend. From this Friday, August 2nd through Sunday, August 4th, many items are tax-exempt, including clothing, diapers and shoes valued at $100 or less; school supplies not exceeding $50 per purchase; computer software that’s $350 or less; personal computers of no more than $1500; graphing calculators at $150 or less; and computer accessories that cost $1500 or less. Missouri is one of 16 states that offers the sales tax exemption for back-to-school purchases, but Illinois hasn’t adopted the holiday. Online purchases are included in the tax-free weekend. Items such as watches, jewelry, handbags, and other items do not qualify.