When we have to pay an amount of money a with b% tax, we have to adition the given percentage in decimal form multiplied by the base amount of money a to the initial money a, like this:
final cost = a+a*b%
In this case, the base cost is $4.56 and the percentage is 0.08 (8%), then we get:
final cost = $4.56 + 4.56*0.08 = $4.9248
Then, 4.56 with 8% tax equals $4.9248
