Is it possible put price on product without tax and show it in the webshop with tax? (Odoo 8)

Because if you put price with tax on product the quotations calculations are incorrect.

EXAMPLE, first way and correct:

Product: Test , price: 2,55 (without tax)

Client: I want 4 Test products

Calculation: 2,55 * 4 = 10,2 --> with tax 10,2 * 1,21 = 12,342 (Rounded Total PRICE: 12,34 €) <----- CORRECT!!!!

This way it doesn't shows on ecommerce the price with tax... but it's the correct

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If you put price on product with TAX, What happens? This price you will put on the price product (with tax), on the backend you need to put on Accounting/Taxes/Taxes "Price included on the price". This way ecommerce shows product price with tax.... but....

Second WAY:

Product: Test , price: 2,55 * 1,21 = 3,0855 --> Rounded to 3,09 (with tax) 

Client: I want 4 Test products

Calculation that Odoo do: 3,09 / 1,21 = 2,55371900826446 * 4 = 10,21487603305784 * 1,21 = 12,35999999999999 (Rounded Total PRICE: 12,36 €) <--- (Odoo get all the decimals) WRONG!!!!!!!!!!!!!!!!!!!

What is the solution ??? T_T