Hi,

I hope you need like this: 

Form view 

Report 

For that you can create two compute fields in purchase.order model, that calculates the sum of each tax groups in the product lines. Then you need to call these fields in the form view and reports. Try like this:

in .py file

class purchase_order(models.Model):
    _inherit = 'purchase.order'
    
    tax_t1 = fields.Float(compute='_compute_tax', string="VAT5%") 
    tax_t2 = fields.Float(compute='_compute_tax', string="VAT20%")    
    
    @api.one
    @api.depends('order_line')
    def _compute_tax(self):
        
        sum_v5 = 0
        sum_v20 = 0
        for rec in self.order_line:
            if rec.taxes_id:
                for tax in rec.taxes_id:
                    if tax.name == "VAT5":
                        sum_v5 = sum_v5 + (rec.price_subtotal * tax.amount)
                    elif tax.name == "VAT20":
                        sum_v20 = sum_v20 + (rec.price_subtotal * tax.amount)
        self.tax_t1 = sum_v5
        self.tax_t2 = sum_v20

in xml view file:

<record id="purchase_order_form_inherited" model="ir.ui.view">
            <field name="name">purchase.order.form.inherited</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                    <field name="amount_tax" position="replace">
                    	<field name="tax_t1" widget="monetary" options="{'currency_field': 'currency_id'}"/>
                    	<field name="tax_t2" widget="monetary" options="{'currency_field': 'currency_id'}"/>
                    </field>
          </field>
       </record>

create an xml file to override the purchase order report (for eg: views/custom_purchase_order.xml) and put the following code:

<openerp>
	<data>
		<template id="report_purchaseorder_document_inherited" inherit_id="purchase.report_purchaseorder_document">
           	<xpath expr="//t/div/div[4]/div/table[@class='table table-condensed']/tr[2]" position="replace">	
						<tr>
                            <td>VAT 5%</td>
                            <td class="text-right">
                                <span t-field="o.tax_t1"
                                    t-field-options='{"widget": "monetary", "display_currency": "o.pricelist_id.currency_id"}'/>
                            </td>
                        </tr>
                        <tr>
                            <td>VAT 20%</td>
                            <td class="text-right">
                                <span t-field="o.tax_t2"
                                    t-field-options='{"widget": "monetary", "display_currency": "o.pricelist_id.currency_id"}'/>
                            </td>
                        </tr>

			</xpath> 
       </template>
	</data>
</openerp>

Don't forget to include this file in __openerp__.py. This will override the purchase order report with new tax fields.

You can also override quotations report similarly.

Hope this helps!

For Odoo 9 in SALE.ORDER ?