Result not valid for sum from another table

Question

I have 2 table

tbl1

INSERT INTO `tbl1` (`id_tbl1`, `name`, `weight`) VALUES
(1, 'data_1', 0.2),
(2, 'data_2', 0.3),
(3, 'data_3', 0.4),
(4, 'data_4', 0.5),
(5, 'data_5', 0.5),
(6, 'data_6', 0.9),
(7, 'data_7', 0.9),
(14, 'data_14', 0.2),
(15, 'data_15', 0.4),
(16, 'data_16', 0.6),
(17, 'data_17', 0.5),
(18, 'data_18', 0.7),
(19, 'data_19', 0.9);

tbl2

INSERT INTO `tbl2` (`id_tbl2`, `id_category`, `id_tbl1`) VALUES
(1, 1, 1),
(2, 1, 2),
(3, 1, 3),
(4, 1, 4),
(5, 1, 5),
(6, 1, 6),
(7, 1, 7),
(14, 3, 14),
(15, 3, 15),
(16, 3, 16),
(17, 3, 17),
(18, 3, 18),
(19, 3, 19);

and this my query

SELECT SUM(weight)  AS 'total'
FROM tbl2
JOIN tbl1 ON tbl2.id_tbl1 = tbl1.id_tbl1 GROUP BY id_category;

Result should be 3.7 and 3.3 but showing

3.6999999999999997
3.3000000000000003

Can somebody tell me what is wrong?

Thank you.