I presume that each gallon has a sale tax. Then we have to find how much is 6% of $5:
[tex]5\times0.06\text{ = \$0,3 (this is the tax value)}[/tex]Then the total price will be:
[tex]2\times(5+0.3)=10.6[/tex]2 gallons that cost $5. And both of them have a sale tax of 6%. The total cost will be $10.6