If you wish to mentally estimate the total cost of items, rounding off the items to the nearest half dollar, then you have to consider all five items separately.
Five items cost $1.85, $.98, $3.49, $9.78, and $6.18.
1. $1.85≈$2;
2. $0.98≈$1;
3. $3.49≈$3.50;
4. $9.78≈$10;
5. $6.18≈$6.
Then the total cost is
$2 + $1 + $3.50 + $10 + $6 =$22.50.
Answer: correct choice is C