Need help with SSRS function

Hello,

Can anyone help me with logic pls.? I have four categories:

--Use Tax = new_usetax

--Sales Tax = new_totaltax

--No Tax

--NULL

I do care about NULL, but i need to create a return if No tax than "Tax Not Included", if Use Tax than $usetax, if Sales Tax than $salestax.

I started, but i stumped. 

=iif(Fields!bmi_taxtypename.Value = "No Tax","Tax Not Included",Fields!new_totaltax.Value)

Help please. Thank you