7,143.66 + 13,674.26 round to the nearest dollar then add

So, first we need to round to the nearest dollar, this means that we need to eliminate the decimal part. The question is: Shall we increase the value of dollars by 1 or keep it as it is??

If the number directly after the decimal point is less than 5, then we will keep the value of the dollars as it is and just eliminate the decimal part.
If the number directly after the decimal point is greater than or equal to 5, then well increment the value of dollars by 1 and eliminate the decimal part.

Applying this to the two values mentioned in the question, we can see that:
7,143.66 is approximately equal to 7,144
13,674.26 is approximately equal to 13,674

Then, we will just add these two values as follows:
7,144 + 13,674 = 20,818