Controls how rounding is performed: - `halfExpand`: Round to the nearest of the values allowed by `roundingIncrement` and `smallestUnit`. When there is a tie, round up. This mode is the default. - `ceil`: Always round up, towards the end of time. - `trunc`: Always round down, towards the beginning of time. - `floor`: Also round down, towards the beginning of time. This mode acts the same as `trunc`, but it's included for consistency with `Temporal.Duration.round()` where negative values are allowed and `trunc` rounds towards zero, unlike `floor` which rounds towards negative infinity which is usually unexpected. For this reason, `trunc` is recommended for most use cases.