Suppress or Override TotalTax field in the Checkout

[dgsweb]

Hi,

I'm using my checkout configuration for my taxes:

- Federal (60%)

- State (17%)

But, I need to change the formula to calculate each tax. I can explain that for the Federal taxes, I considered (total products + shipping) in the calculation, but for the State taxes, I considered only the total products field and did not include shipping. 

Is it possible to change the calculation way for each tax type?

Assume I create a custom app. Is it possible to override the field TotalTax with my manual calculation?

Thanks,

Douglas