eiru_hide_Tax/views/purchase_view.xml

<openerp>
    <data>
        <record model="ir.ui.view" id="purchase_order_inherit">
            <field name="name">purchase.order.inherit</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//tree/field[@name='taxes_id']" position="attributes">
                    <attribute name="invisible">True</attribute>
                </xpath>
                
                <xpath expr="//field[@name='amount_untaxed']" position="attributes">
                    <attribute name="string">Subtotal</attribute>
                </xpath>
                <xpath expr="//field[@name='amount_tax']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
                
            </field>
        </record>

        <record model="ir.ui.view" id="purchase_order_line_inherit">
            <field name="name">purchase.order.line.inherit</field>
            <field name="model">purchase.order.line</field>
            <field name="inherit_id" ref="purchase.purchase_order_line_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='taxes_id']" position="attributes">
                    <attribute name="invisible">True</attribute>
                </xpath>
            </field>
        </record>

        <record model="ir.ui.view" id="purchase_order_tree_inherit">
            <field name="name">purchase.order.tree.inherit</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_tree"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='amount_untaxed']" position="attributes">
                    <attribute name="invisible">True</attribute>
                </xpath>
            </field>
        </record>

        <template id="purchase_tax_hide" inherit_id="purchase.report_purchaseorder_document">
            <xpath expr="//table/thead/tr/th[2]" position="replace"/>
            <xpath expr="//table/tbody/tr/td[2]" position="replace"/>
            <xpath expr="//div/div/table/tr[2]" position="replace"/>
            <xpath expr="//div/div/table/tr[1]" position="replace"/>
        </template>
    </data>
</openerp>