When adding with differences in significant figures, should you round first?
For example, $3.4698 + 2.11 = 5.57$ according to the rules shown in Wikipedia. But in reality, it is closer to $5.58$, as $3.4698$ can be rounded to $3.47$. So which is the correct method?
The rule from Wikipedia is " the result is rounded to the last digit that is significant in each of the numbers being summed.". You perform the calculation with all the numbers you have and round the result. This would give $5.58$ in your example.