Look at the 4th decimal place to decide whether to round up or down.
• 12.1999: the first three decimal places are 1-9-9.
• The 4th decimal digit is 9, which is ≥ 5, so we round up.
• 12.199 rounds up: the third 9 becomes 10, carrying to the second 9 → 12.200
Final Answer: C: 12.200