[FIX] point_of_sale: round globally
[FIX] point_of_sale: round globally

Commit 06754b32 brings an inconsistency between the PoS frontend, the
pos_order and the account_invoice tax calculation. Part of the commit is
correct since it corrects the matching between the `compute_all`
methods, however.

opw-680891

bplancher/odoo,laslabs/odoo,ygol/odoo,dfang/odoo,microcom/odoo,bplancher/odoo,storm-computers/odoo,Elico-Corp/odoo_OCB,ygol/odoo,microcom/odoo,hip-odoo/odoo,Elico-Corp/odoo_OCB,hip-odoo/odoo,laslabs/odoo,storm-computers/odoo,laslabs/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,hip-odoo/odoo,ygol/odoo,dfang/odoo,laslabs/odoo,dfang/odoo,Elico-Corp/odoo_OCB,microcom/odoo,dfang/odoo,laslabs/odoo,storm-computers/odoo,bplancher/odoo,Elico-Corp/odoo_OCB,storm-computers/odoo,ygol/odoo,bplancher/odoo,hip-odoo/odoo,laslabs/odoo,microcom/odoo,hip-odoo/odoo,microcom/odoo,Elico-Corp/odoo_OCB,hip-odoo/odoo,bplancher/odoo,microcom/odoo,ygol/odoo,ygol/odoo,ygol/odoo,dfang/odoo,storm-computers/odoo,storm-computers/odoo,dfang/odoo