I am doing the following:

1. Get the property with Nested Content
2. Pass it into a partial
3. Render Grid

View

@Html.Partial("Components/ContentTabs", Model.ContentTabs)

Partial

@model IEnumerable<IPublishedContent>
@if (Model.Any()) 
{
<div>
    @* List each piece of nested content *@
    <ul>
        @{
            var i = 0;
            foreach (var node in Model)
            {
                i++;
                <li>@i</li>
                @* you can get your properties here too *@
            }
        }
    </ul>
</div>
<div>
    @* Render the Grid on each piece of Content *@
    @{
        var c = 0;
        foreach (var node in Model)
        {
            c++;
            @Html.GetGridHtml(node.GetProperty("contentGrid"))
        }
    }
</div>
}

However, you could probably just do (untested)

@{
    var nestedContent = Model.Content.GetPropertyValue<IEnumerable<IPublishedContent>>("contentTabs");

    foreach (var item in nestedContent)
    {
        @Html.GetGridHtml(item.GetProperty("contentGrid"));
    }
}