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
for candidate_moves in candidate_moves_list:
            # 
            for k, g in groupby(sorted(candidate_moves, key=self._prepare_merge_move_sort_method), key=itemgetter(*distinct_fields)):
                moves = self.env['stock.move'].concat(*g).filtered(lambda m: m.state not in ('done', 'cancel', 'draft'))
                # 
                if len(moves) > 1:
                    moves_to_merge.append(moves)
        # 
        for moves in moves_to_merge:
            # 
            moves.mapped('move_line_ids').write({'move_id': moves[0].id})
            # 
            moves[0].write(moves._merge_moves_fields())
            # 
            moves_to_unlink |= moves[1:]
        if moves_to_unlink:
            # 
            moves_to_unlink.write({'propagate': False})
            moves_to_unlink._action_cancel()
            moves_to_unlink.unlink()
        return (self | self.env['stock.move'].concat(*moves_to_merge)) - moves_to_unlink
    def _get_relevant_state_among_moves(self):
        # 
        #     
        #     
        #     
        #     
        #     
        #     
        #