Hi,
If you want to have rounded corners only with CSS, IE pre9 will indeed require an htc file.
Alternatively, you can make your rounded corners in JS which won't require that htc file. There are several method out there:
www.curvycorners.net/
jquery.malsup.com/corner/
www.html.it/articoli/nifty/index.html
In all of these examples, you will have to use divs for your buttons. By default, the two button mode of hikashop (normal or CSS) use either an input or a link. If you want to change and use a div, you will need to define the function hikashop_button_render in the file templates/YOUR_TEMPLATE/html/hikashop_button.php basing your code on the code available in the file administrator/components/com_hikashop/helpers/cart.php
So it's not that easy.
Another easier way will be to use images, etc. For a complete list of rounded corners technics you can look at that page:
www.devwebpro.com/25-rounded-corners-techniques-with-css/
In HikaShop, we decided to not use any specific rounded corner code, so the rounded corners that you can set on the div layouts won't work for IE per 9 unless you setup an htc file.
