You can put the grid inside a rounded border, but this puts a round border around all 4 corners.
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sf="http://schemas.syncfusion.com/wpf"
Title="Window1" Height="300" Width="300">
HorizontalAlignment="Center" VerticalAlignment="Center">
HorizontalScrollBarVisibility="Visible"
VerticalScrollBarVisibility="Visible">