You can use
SCOPE_IDENTITY[
^] to get the recent generated Id. Here is a sample approach
INSERT INTO sell_master ( mn_sell_amount) VALUES (500)
DECLARE @in_sell_id INT
SET @in_sell_id = SCOPE_IDENTITY()
INSERT INTO sell_detail(in_sell_id, vc_item_name) VALUES (@in_sell_id,'juice')
INSERT INTO sell_detail(in_sell_id, vc_item_name) VALUES (@in_sell_id,'sweets')