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
""" Try to assign the moves to an existing picking that has not been
        reserved yet and has the same procurement group, locations and picking
        type (moves should already have them identical). Otherwise, create a new
        picking to assign them to. """
        Picking = self.env['stock.picking']
        for move in self:
            recompute = False
            picking = Picking.search([
                ('group_id', '=', move.group_id.id),
                ('location_id', '=', move.location_id.id),
                ('location_dest_id', '=', move.location_dest_id.id),
                ('picking_type_id', '=', move.picking_type_id.id),
                ('printed', '=', False),
                ('state', 'in', ['draft', 'confirmed', 'waiting', 'partially_available', 'assigned'])], limit=1)
            if picking:
                if picking.partner_id.id != move.partner_id.id or picking.origin != move.origin:
                    # 
                    # 
                    # 
                    picking.write({
                        'partner_id': False,
                        'origin': False,
                    })
            else:
                recompute = True
                picking = Picking.create(move._get_new_picking_values())