how do you default tax from an item's set-up to the sales order line?

I am trying to default tax for an item for the Order to Cash cycle.

On the item, I have populated the Output Tax Classification Code field with a Tax Code.  When I enter a Receivables transaction for this item number, the tax code defaults.  However, when I enter a sales order line for this item, the associated tax does not default and it is not populated through the shipping/auto invoice process either.

Any help would be greatly appreciated.

Thanks,

Susan