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
# 
                if move.product_id.tracking == 'serial' and (move.picking_type_id.use_create_lots or move.picking_type_id.use_existing_lots):
                    for i in range(0, int(move.product_qty - move.reserved_availability)):
                        self.env['stock.move.line'].create(move._prepare_move_line_vals(quantity=1))
                else:
                    to_update = move.move_line_ids.filtered(lambda ml: ml.product_uom_id == move.product_uom and
                                                            ml.location_id == move.location_id and
                                                            ml.location_dest_id == move.location_dest_id and
                                                            ml.picking_id == move.picking_id and
                                                            not ml.lot_id and
                                                            not ml.package_id and
                                                            not ml.owner_id)
                    if to_update:
                        to_update[0].product_uom_qty += move.product_qty - move.reserved_availability
                    else:
                        self.env['stock.move.line'].create(move._prepare_move_line_vals(quantity=move.product_qty - move.reserved_availability))
                assigned_moves |= move
            else:
                if not move.move_orig_ids:
                    if move.procure_method == 'make_to_order':
                        continue
                    # 
                    available_quantity = self.env['stock.quant']._get_available_quantity(move.product_id, move.location_id)
                    if available_quantity <= 0:
                        continue
                    need = move.product_qty - move.reserved_availability
                    taken_quantity = move._update_reserved_quantity(need, available_quantity, move.location_id, strict=False)
                    if float_is_zero(taken_quantity, precision_rounding=move.product_id.uom_id.rounding):
                        continue
                    if need == taken_quantity: