Cumulative tax and Round prices during calculations no function

-- HikaShop version -- : 4.7.5
-- Joomla version -- : 3.9.21
-- PHP version -- : 7.2.34

Greeting Hikashop Surpport,

We had met two problem in hikashop:

1) Cumulative tax no function
- In Service Tax 8%, we want to subtotal + Service Charge 10% then multiply by 8%. Thus, we open the Cumulative tax. However, it doesn't work.

- For example in second attachment, the Service Tax 8% should be RM2.36 ((RM26.80 + RM2.68) * 0.08), not RM2.14 (RM26.80 * 0.08)

- Furthermore, if I close the Service Charge 10%'s Cumulative tax, the Service Tax 8% will disappear

2) Round prices during calculations no function
- We need a function to round up the total price. Thus, we open the Round prices during calculations. However, it doesn't work

- For example, if the total price is RM21.44 which is less then 0.05, will round up to RM21.40; if the total price is RM20.45 which is more than equal to 0.05, will round up to RM20.50.
- Another example in second attachment, the total price RM31.62 should be round up to RM31.60

That's all our problem