https://github.com/odoo/odoo/blob/b192431aeecc59b48898ce9c6f276b82d65cbfa6/addons/stock/models/stock_move.py#L1026

rounding_method ='UP'
I think it **need be changed to:**
rounding_method ='HALF-UP'

I get this message then I Verify new Delivery(stock.picking):

> The initial demand has been updated.
> My Product
> Quantity : 5.951 -> 5.949999999999999 

and
> The initial demand has been updated.
> My Product
> Quantity : 5.951 -> 5.951 


How I did it(you can also repeat this error): Create new Product > add Qty on hand > Create SO > Add Product with quantity 5.5 > Verify > open Delivery > add Delivered qty 5.95 > Verify > Get trouble: odoo change my qty to 5.951
![default](https://user-images.githubusercontent.com/34191760/39213952-9b246470-481b-11e8-8e06-a074b1044536.png)

You can try execute in python:
5.95 - 5.5 = 0.4500000000000002

Look at the code:
```
            extra_move_quantity = float_round(
                self.quantity_done - self.product_uom_qty,
                precision_rounding=self.product_uom.rounding,
                rounding_method ='UP')
```
if you setup parameters like this:
```
            0.451 = float_round(
                5.95 - 5.5,
                precision_rounding=self.product_uom.rounding,
                rounding_method ='UP')
```
Then you get 0.451.  This is wrong!
Try:
```
            0.45 = float_round(
                5.95 - 5.5,
                precision_rounding=self.product_uom.rounding,
                rounding_method ='HALF-UP')
```
0.45 = 5.95 - 5.5
addons/stock/tests/test_move2.py
""" Check the good behavior of creating an extra move in a delivery order. This usecase
        simulates the delivery of 2 item while the initial stock move had to move 1 and there's
        only 1 in stock.
        """
        delivery_order = self.env['stock.picking'].create({
            'location_id': self.pack_location,
            'location_dest_id': self.customer_location,
            'partner_id': self.partner_delta_id,
            'picking_type_id': self.picking_type_out,
        })
        move1 = self.MoveObj.create({
            'name': self.productA.name,
            'product_id': self.productA.id,
            'product_uom_qty': 1,
            'product_uom': self.productA.uom_id.id,
            'picking_id': delivery_order.id,
            'location_id': self.pack_location,
            'location_dest_id': self.customer_location,
        })
        
        pack_location = self.env['stock.location'].browse(self.pack_location)
        self.env['stock.quant']._update_available_quantity(self.productA, pack_location, 1)
        self.assertEqual(self.env['stock.quant']._get_available_quantity(self.productA, pack_location), 1.0)
        # as
        delivery_order.action_confirm()
        delivery_order.action_as()