If the business requirement is for the record to be exactly 9 rubles, and not 10, what should be done?

If the business requirement is for the record to be exactly 9 rubles, and not 10, then it is necessary to ensure precise representation and processing of monetary values without rounding up. In Java, it is recommended to use the BigDecimal class for working with monetary amounts, as it allows for accurate storage and manipulation of decimal numbers.

Example:

import java.math.BigDecimal;

BigDecimal amount = new BigDecimal("9.00");
// Use BigDecimal methods for arithmetic, avoiding double or float

If the data comes from a source with rounding, you need to check the conversion logic and ensure that automatic rounding to 10 does not occur. It is also worth clarifying how exactly the business defines the amount — perhaps by using the setScale method with the appropriate rounding mode, such as RoundingMode.DOWN, to always round down:

amount = amount.setScale(2, RoundingMode.DOWN);

This way, you guarantee that the amount will not exceed 9 rubles.