Answer:
$3.79/$4.55
Explanation:
1. How many liters in a gallon: 3.79 l (US), 4.55 l (Imp)
2. Cost of gas/gallon: 3.79 liter * $1/liter = $3.79 (US), $4.55 (Imp)
From what you say, using the US gallon, since both answers round to the same number (since there is no currency below the cent), it wouldn't matter too much. Also, unit conversions should not lead to different answers.