There is no “correct” mode, it depends on the business case. Examples:
- When calculating annual taxes, the fractions are often cut off (
RoundingMode.FLOOR). - When calculating a bonus, you might want to always round in favor of the customer (
RoundingMode.CEILING). - For taxes on a bill, you usually round
HALF_UP - When doing complex financial simulations, you don’t want to round at all.
The documentation of RoundingMode contains a lot of examples how the different modes work.
To get a better answer, you must tell us what you want to achieve.
That said, BigDecimal is the correct type to use in Java because it can preserve any amount of precision plus it lets you chose the rounding mode most suitable for your case.