DECLARE  @tv_Transactions TABLE
(
	ID		int,
	CustomerID	varchar(25),
	TransactionDay	datetime,
	Sequence	int
);

INSERT @tv_Transactions (ID, CustomerID, TransactionDay, Sequence)
SELECT 1, 'I100000999', '2007-07-23 00:00:00.000', 1 UNION ALL
SELECT 2, 'I100000999', '2007-07-25 00:00:00.000', 2 UNION ALL
SELECT 3, 'I100000999', '2008-05-17 00:00:00.000', 3 UNION ALL
SELECT 4, 'I100000999', '2008-05-25 00:00:00.000', 4 UNION ALL
SELECT 5, 'I100000999', '2008-06-01 00:00:00.000', 5 UNION ALL
SELECT 6, 'I100000999', '2008-07-04 00:00:00.000', 6 UNION ALL
SELECT 7, 'I100000997', '2007-12-02 00:00:00.000', 1 UNION ALL
SELECT 8, 'I100000997', '2007-12-11 00:00:00.000', 2;


WITH TranDays (ID, CustomerID, TransactionDay, NextID, NextTransactionDay, Days) AS
(
	SELECT  a.ID, a.CustomerID, a.TransactionDay, 
			b.id as NextID, b.transactionday as NextTransactionDay,
			DATEDIFF(dd, a.transactionday, b.transactionday) as Days
	FROM @tv_Transactions a
	LEFT JOIN @tv_Transactions b
		ON a.customerid = b.customerid AND b.transactionday > a.transactionday
)

SELECT ID, CustomerID, TransactionDay
	FROM TranDays
	WHERE Days BETWEEN 1 AND 10
UNION
SELECT NextID AS ID, CustomerID, NextTransactionDay AS TransactionDay
	FROM TranDays
	WHERE Days BETWEEN 1 AND 10;

SELECT CustomerID,
      (DATEDIFF(dd,TransactionDay,Start)/9 + 1) AS Group,
       MIN(TransactionDay) AS GroupStart
       MAX(TransactionDay) AS GroupEnd
FROM
(
SELECT ID,
	CustomerID,
	TransactionDay,
	Sequence,
        MIN(TransactionDay) OVER(PARTITION BY CustomerID) AS Start
FROm YourTable
)t
GROUP BY CustomerID,DATEDIFF(dd,TransactionDay,Start)/9