Taxble & Non Taxble Items

Hi Gurus,

Please help me over the following issue.

We create an invoice with taxable and non taxbale iitems. But system calculates the tax  for both itmes  non taxible items and taxable items.

Inorder to prevent the tax calcualationfor non taxable items, user needs to change the tax code ( No tax code) every time.

Is there any setup that no tax code gets defalut automatically for non taxble items at invoice line level?

Regards,

Srini