The sales tax is the additional cost with a value of a fraction of the gross cost. Let's compute first the gross cost:
Gross cost = 3($1.59) + 2($3.25) = $11.27
The sales tax is, therefore, 7.25% of $11.27.
Sales Tax cost = $11.27(0.0725) = $0.817
The total purchase is equal to the gross cost and the sales tax cost.
Total Purchase Cost = $11.27 + $0.817 = $12.09