Doubt In Rollback Transactions

may be an idiotic question

I have created a table test1 with primary key as given below. I have written a procedure to insert rows. is the rollback transaction given under is correct?. (OR) shall i give the rollback only once at the end?

need more explanation on the rollback transaction.



CREATE TABLE [TEST1] (
[COL1] [varchar] (50) NOT NULL
) ON [PRIMARY]
GO


ALTER TABLE [TEST1] WITH NOCHECK ADD
CONSTRAINT [PK_TEST1] PRIMARY KEY CLUSTERED
(
[COL1]
) ON [PRIMARY]
GO


ALTER PROCEDURE T AS
BEGIN TRANSACTION
INSERT INTO TEST1 VALUES('A')
IF (@@ERROR <> 0) GOTO ERR
INSERT INTO TEST1 VALUES('B')
IF (@@ERROR <> 0) GOTO ERR
INSERT INTO TEST1 VALUES('B')
IF (@@ERROR <> 0) GOTO ERR
INSERT INTO TEST1 VALUES('C')
IF (@@ERROR <> 0) GOTO ERR
INSERT INTO TEST1 VALUES('D')
IF (@@ERROR <> 0) GOTO ERR
ERR:
IF (@@ERROR <> 0)
ROLLBACK TRANSACTION
else
COMMIT TRANSACTION