A lot of investigation on CSS and finally i came to the point that at this time round curve border with CSS not possible. We have to use image for round curve effect. However, According to W3C CSS3.0 specification it will be possible in near future with border-radius? property. CSS3.0 still in draft status so this property not compatible with available browser this time.
Border Radius Property Syntax:
border-radius: <length> <length>
Individual corners Property Syntax:
While googling i found few interesting URL that might be useful for the visitors who want to implement round corner border anyway.
Tool to generate HTML/CSS code and images for rounded corners:
CSS Rounded Corner Border Tricks: