Americans once dumped an entire shipment of tea into Boston Harbor to show their frustration at paying taxes.No such effort will be needed to avoid paying sales tax on school supplies this weekend as Tennessee conducts its annual tax-free holiday.The state’s sales-tax holiday begins Friday at 12:01 a.m., and ends Sunday at 11:59 p.m. Tax-free items include:• Clothing $100 or less• School supplies $100 or less• Computers $1,500 or lessThe National Retail Federation estimates families with K-12 kids will spend an average of $673 this year on back-to-school shopping. That’s up from an average of $630 last year, the organization says.A McMinnville family which spends the National Retail Federation average of $673 will save $65.61 in taxes based on the city’s current sales tax rate.