The discount is 15%. This means that they paid 85% of the original price ( 100% - 15% = 85%)
Multiply the original price by 85% to find the discounted price:
14.99 x 0.85 = $12.74
Now multiply the discounted price by 5% to find the sales tax, then add that to the price:
12.74 x 0.05 = 0.637 = 0.64 ( amount of sales tax)
Total: 12.74 + 0.64 = $13.38