A sales tax rate of 6.25% means that 6.25 cents is going to be charged for tax for each dollar you spend. (Because 6.25% of $1.00 is 6.25 cents.)
If he was spending $10, the sales tax would be 62.5 cents (6.25 cents per dollar x 10 dollars). Since he is spending $60 on this item, the equation would be (6.25 cents per dollar x 60 dollars) (6.25 cents x 60 = 375 cents).