=item taxnum - primary key (assigned automatically for new tax rates)
+=item district - tax district (optional)
+
=item city
=item county
$self->exempt_amount(0) unless $self->exempt_amount;
$self->ut_numbern('taxnum')
+ || $self->ut_alphan('district')
|| $self->ut_textn('city')
|| $self->ut_textn('county')
|| $self->ut_anything('state')