'invisible' is not propagated from the model to the view

Anyway, set the field readonly is better than invisible because
it is still interesting to see this value even if it cannot be changed

account_compute_tax_amount/account_move_line.py

@@ -27,8 +27,8 @@ from openerp import models, fields, api
 class AccountMoveLine(models.Model):
     _inherit = "account.move.line"
 
-    # We set the tax_amount invisible, because we recompute it in every case.
-    tax_amount = fields.Float(invisible=True)
+    # We set the tax_amount readonly, because we recompute it in every case.
+    tax_amount = fields.Float(readonly=True)
 
     @api.one
     def force_compute_tax_amount(self):