ListBox scrollbar breaks sync columns with Grid.IsSharedSizeScope

Question

I need to show a table with headers using ListBox

I searched on the web about how to create this and i found this answer, here is the XAML code i created:

<Grid Grid.Row="1" Grid.IsSharedSizeScope="True">
    <Grid.RowDefinitions>
        <RowDefinition Height="*"></RowDefinition>
        <RowDefinition Height="6*"></RowDefinition>
    </Grid.RowDefinitions>
    <Grid Grid.Row="0" ShowGridLines="True">
        <Grid.ColumnDefinitions>
            <ColumnDefinition SharedSizeGroup="quantityColumn"></ColumnDefinition>
            <ColumnDefinition SharedSizeGroup="priceColumn"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition SharedSizeGroup="editColumn"></ColumnDefinition>
            <ColumnDefinition SharedSizeGroup="deleteColumn"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <TextBlock Grid.Column="0" Foreground="#5a5a5a" TextAlignment="Center" Margin="1" VerticalAlignment="Center">Cantidad</TextBlock>
        <TextBlock Grid.Column="1" Foreground="#5a5a5a" TextAlignment="Center" Margin="1" VerticalAlignment="Center">Precio</TextBlock>
        <TextBlock Grid.Column="2" Foreground="#5a5a5a" TextAlignment="Center" Margin="1" VerticalAlignment="Center">Descripción</TextBlock>
        <TextBlock Grid.Column="3" Foreground="#5a5a5a" TextAlignment="Center" Margin="1" VerticalAlignment="Center">Editar</TextBlock>
        <TextBlock Grid.Column="4" Foreground="#5a5a5a" TextAlignment="Center" Margin="1" VerticalAlignment="Center">Eliminar</TextBlock>
    </Grid>
    <ListBox Grid.Row="1" HorizontalContentAlignment="Stretch" ScrollViewer.HorizontalScrollBarVisibility="Hidden" ScrollViewer.VerticalScrollBarVisibility="Auto" Name="OrderList" Background="Transparent" BorderBrush="{x:Null}" ManipulationBoundaryFeedback="OrderList_ManipulationBoundaryFeedback">
        <ListBox.ItemContainerStyle>
            <Style TargetType="{x:Type ListBoxItem}">
                <Setter Property="Focusable" Value="False"/>
                <EventSetter Event="RequestBringIntoView" Handler="ListBoxItem_RequestBringIntoView"/>
            </Style>
        </ListBox.ItemContainerStyle>
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid ShowGridLines="True">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition SharedSizeGroup="quantityColumn"></ColumnDefinition>
                        <ColumnDefinition SharedSizeGroup="priceColumn"></ColumnDefinition>
                        <ColumnDefinition Width="*"></ColumnDefinition>
                        <ColumnDefinition SharedSizeGroup="editColumn"></ColumnDefinition>
                        <ColumnDefinition SharedSizeGroup="deleteColumn"></ColumnDefinition>
                    </Grid.ColumnDefinitions>
                    <TextBlock Grid.Column="0" Foreground="White" TextAlignment="Center" Margin="7">Cantidad</TextBlock>
                    <TextBlock Grid.Column="1" Foreground="White" TextAlignment="Center" Margin="7">Precio</TextBlock>
                    <TextBlock Grid.Column="2" Foreground="White" TextAlignment="Center" Margin="7">Descripción</TextBlock>
                    <TextBlock Grid.Column="3" Foreground="White" TextAlignment="Center" Margin="7">Editar</TextBlock>
                    <TextBlock Grid.Column="4" Foreground="White" TextAlignment="Center" Margin="7">Eliminar</TextBlock>
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
</Grid>

And here is the c# code i created to test and populate the ListBox

List<OrderItem> orders = new List<OrderItem>();
orders.Add(new OrderItem() { a = "wash", b = "b" });
orders.Add(new OrderItem() { a = "the", b = "c" });
orders.Add(new OrderItem() { a = "car", b = "d" });
orders.Add(new OrderItem() { a = "wash", b = "b" });
OrderList.ItemsSource = orders;

Since the ListBox only shows 4 rows, it doesnt have to set a scrollbar, and the headers are almost 100% aligned with the table columns:

The problem worsens when i add more rows to the ListBox and the scrollbar appears:

As you can see the offset of each column with its header its too big. How can i tell the Grid.IsSharedSizeScope to be aware of the width of the scrollbar and to consider it to the headers width? What i need it's to have the table columns 100% aligned with the table headers.