The following code uses the RoundRect API function. The last two parameters give the width and height of an ellipse that defines the corner rounding. Note that a corner essentially uses a quarter of the ellipse so the rounded parts are half as wide and tall as the ellipse.

Private Sub cmdPrintVbStyle_Click()
Dim x1 As Long, y1 As Long, x2 As Long, y2 As Long, x3 As _
    Long, y3 As Long

    ' Print something to initialize the printer.
    Printer.CurrentX = 1440
    Printer.CurrentY = 1440
    Printer.Print " "

    ' Upper left corner.
    x1 = 1440 / Printer.TwipsPerPixelX          ' 1 inch
    y1 = 1440 / Printer.TwipsPerPixelY          ' 1 inch
    ' Lower right corner.
    x2 = 5 * 1440 / Printer.TwipsPerPixelX      ' 5 inches
    y2 = 3 * 1440 / Printer.TwipsPerPixelY      ' 3 inches
    ' Width and height of the corner ellipse.
    x3 = 1440 / Printer.TwipsPerPixelX          ' 1 inch
    y3 = 0.5 * 1440 / Printer.TwipsPerPixelY    ' 0.5 inch

    ' Draw the rounded rectangle.
    RoundRect Printer.hdc, x1, y1, x2, y2, x3, y3

    Printer.EndDoc
End Sub