By rounding to the nearest liter, the question is asking us to round to the nearest whole number (get rid of any numbers after the decimal point). This means that we want the last number of our answer to be the number just to the left of the decimal point, which is a 3.
To determine if we should leave the number or round it up, we look to the number to the right of the 3 which is a 4. Because 4 is less than 5, we do not round up. Therefore, the answer would be 103 liters.