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/models/stock_move.py
# 
            # 
            # 
            # 
            # 
            taken_quantity = 0
        # 
        for reserved_quant, quantity in quants:
            to_update = self.move_line_ids.filtered(lambda m: m.product_id.tracking != 'serial' and
                                                    m.location_id.id == reserved_quant.location_id.id and m.lot_id.id == reserved_quant.lot_id.id and m.package_id.id == reserved_quant.package_id.id and m.owner_id.id == reserved_quant.owner_id.id)
            if to_update:
                to_update[0].with_context(bypass_reservation_update=True).product_uom_qty += self.product_id.uom_id._compute_quantity(quantity, self.product_uom, rounding_method='HALF-UP')
            else:
                if self.product_id.tracking == 'serial':
                    for i in range(0, int(quantity)):
                        self.env['stock.move.line'].create(self._prepare_move_line_vals(quantity=1, reserved_quant=reserved_quant))
                else:
                    self.env['stock.move.line'].create(self._prepare_move_line_vals(quantity=quantity, reserved_quant=reserved_quant))
        return taken_quantity
    def _action_assign(self):
        """ Reserve stock moves by creating their stock move lines. A stock move is
        considered reserved once the sum of `product_qty` for all its move lines is
        equal to its `product_qty`. If it is less, the stock move is considered
        partially available.
        """
        assigned_moves = self.env['stock.move']
        partially_available_moves = self.env['stock.move']
        for move in self.filtered(lambda m: m.state in ['confirmed', 'waiting', 'partially_available']):
            if move.location_id.usage in ('supplier', 'inventory', 'production', 'customer')\
                    or move.product_id.type == 'consu':