为什么 sql server 很难舍入浮点数？

    if exists (select 1 from sys.tables where name = 'd_ratio') begin drop table d_ratio end
    if exists (select 1 from sys.tables where name = 'elrd') begin drop table elrd end

    CREATE TABLE [dbo].[d_ratio](
        [index] [bigint] NULL,
        [Class] [bigint] NULL,
        [Dratio] [float] NULL,
        [ELR-Act1] [float] NULL,
        [ELR-Act2] [float] NULL
    ) ON [PRIMARY]
    GO

    Insert into D_ratio
    select 0,2503,0.285,0.75,1.33

    CREATE TABLE [dbo].[ELRD](
        [RATE_EFFDT] [date] NOT NULL,
        [CLASS] [varchar](4) NOT NULL,
        [ELR] [decimal](5, 2) NULL,
        [D_RATIO] [decimal](5, 2) NULL,
        [EXPO_ACT] [char](2) NOT NULL
    ) ON [PRIMARY]
    GO

    truncate table elrd
    insert into elrd(Rate_effdt, class, elr, d_ratio, EXPO_ACT)
    select getdate(), right('0000' + cast(class as varchar(10)),4), round(cast([ELR-Act1] as decimal(10,3)),2),Dratio, 1
    from d_ratio

    select Dratio, * from d_ratio
    select D_ratio, * from elrd

输入为 0.285，输出为 0.28。

但是，如果我将其转换为精度为 3 点的小数，如下所示：

    truncate table elrd
    insert into elrd(Rate_effdt, class, elr, d_ratio, EXPO_ACT)
    select getdate(), right('0000' + cast(class as varchar(10)),4), round(cast([ELR-Act1] as decimal(10,3)),2), cast(dratio as decimal(10,3)), 1
    from d_ratio

它以 0.285 的形式输入，以 0.29 的形式输出 - 它被正确地四舍五入。

问题SQL Server 在做什么？它是截断浮点数和舍入小数吗？