Devon is buying 3 greeting cards that cost $0.97 each. How can rounding be used to estimate the total cost of the cards? Since each card is about $1, the total cost is approximately 3 + 1 = $4. Since each card is about $1, the total cost is approximately 3 × 1 = $3. Since he is buying about 10 cards, the total cost is approximately 10 × 0.97 = $9.70. Since he is buying about 10 cards, the total cost is approximately 10 + 0.97 = $10.97.