To calculate the sales tax you first have to do this calculation
$299.99 x .06. You would choose .06 because 6% converted into decimal form is .06.
The total for this calculation would be 17.9994, which would round to $18.00.
Now you apply the amount of this calculation to the original amount.
$299.99 + $18.00 = $317.99
The total cost including sales tax would be $317.99
I hope this helped!