Question 370150
Typically since you only have 1 decimal place you don't extend it. 
If you have more decimal places, you can round up. 
So as an example, 
{{{23.1837}}} to the nearest thousandth would be 
{{{23.184}}}
However, 549.5 does not equal 549.500 because now you're implying that you have that much precision in your measurement where you may not really have it. Like if I was measure my height with a tape measure I could say my height was 76 1/2 inches. 
That doesn't mean my height is 76.500 inches because my tape measure doesn't have a precision down to 0.001.