SQL Server 2017

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

create table tempcust (
    id int,
    name nvarchar(50),
    amount nvarchar(50),
    groupid int
)

insert into tempcust (id,name,amount)    
values
    (1, 'Bob Smith',    '$50.12'),
    (2, 'Bob Smith',    '$12.33' ),
    (3, 'Bob Smith',    '$33.12' ),
    (4, 'Bob Smith',    '$14.86' ),
    (5, 'Bob Smith',    '$6.36' ),
    (6, 'Bob Smith',    '$2.14'),
    (7, 'Bob Smith',    '$10.64'),
    (8, 'Bob Smith',    '$19.14'),
    (9, 'Bob Smith',    '$27.64'),
    (10,    'Bob Smith',    '$36.14'),
    (11,    'Bob Smith',    '$44.64'),
    (12,    'Bob Smith',    '$53.14'),
    (13,    'Jane Doe', '$14.86' ),
    (14,    'Jane Doe', '$6.36'),
    (15,    'Jane Doe', '$2.14'),
    (16,    'Jane Doe', '$10.64'),
    (17,    'Jane Doe', '$19.14'),
    (18,    'Jane Doe','$27.64'),
    (19,    'Jane Doe', '$36.14'),
    (20,    'Kylie Robinson',   '$5.00') ,
    (21,    'Kylie Robinson',   '$6.00' ),
    (22,    'Kylie Robinson',   '$7.00' ),
    (23,    'Kylie Robinson',   '$8.00' ),
    (24,    'Kylie Robinson',   '$9.00' );

24 rows affected

id	name	amount	groupid	prev_name	within_name_groupId	min_grp_id	groupid
1	Bob Smith	$50.12	null	null	1	1	1
2	Bob Smith	$12.33	null	Bob Smith	1	1	1
3	Bob Smith	$33.12	null	Bob Smith	1	1	1
4	Bob Smith	$14.86	null	Bob Smith	1	1	1
5	Bob Smith	$6.36	null	Bob Smith	1	1	1
6	Bob Smith	$2.14	null	Bob Smith	2	6	2
7	Bob Smith	$10.64	null	Bob Smith	2	6	2
8	Bob Smith	$19.14	null	Bob Smith	2	6	2
9	Bob Smith	$27.64	null	Bob Smith	2	6	2
10	Bob Smith	$36.14	null	Bob Smith	2	6	2
11	Bob Smith	$44.64	null	Bob Smith	3	11	3
12	Bob Smith	$53.14	null	Bob Smith	3	11	3
13	Jane Doe	$14.86	null	Bob Smith	1	13	4
14	Jane Doe	$6.36	null	Jane Doe	1	13	4
15	Jane Doe	$2.14	null	Jane Doe	1	13	4
16	Jane Doe	$10.64	null	Jane Doe	1	13	4
17	Jane Doe	$19.14	null	Jane Doe	1	13	4
18	Jane Doe	$27.64	null	Jane Doe	2	18	5
19	Jane Doe	$36.14	null	Jane Doe	2	18	5
20	Kylie Robinson	$5.00	null	Jane Doe	1	20	6
21	Kylie Robinson	$6.00	null	Kylie Robinson	1	20	6
22	Kylie Robinson	$7.00	null	Kylie Robinson	1	20	6
23	Kylie Robinson	$8.00	null	Kylie Robinson	1	20	6
24	Kylie Robinson	$9.00	null	Kylie Robinson	1	20	6