Problem with total calculation

[forever21]

Well.. i had already found this problem, but had found also a walkaround...
The thing was that the totals had diferente cost in one place and in another..., after asking here in th forum, i decided to disable the shipping cost, and changed the taxes type from % to $, and used that tax as a shipping cost.
Well.. after all this, now I need to be able to have items with free shipping ,but as i said, i was using a tax as shipping cost... so..., i had to turn shipping on again, and had to use the taxes in its primary function... but I still have the problem!
I know my English is no too good... so i'm sending you two images, it sais more than 1000 words...
Hope you could find the problem.
Greetings!!

[forever21]

Well, making some tests, I just turned off the taxes, and used both the free shipping option and the flat shipping cost and its working fine.
I think the first time the free shipping option didn't work 'cause i had something configured in the product tab.
Anyway... it would be great if someone can find a solution to the issue showed in the images.
Thank you very much...
See you around!