Obviously, in the HikaShop system main configuration you have set a thumbnail size of only 100x100px, but your template CSS is forcing them to 100% of the parent container width, which in product listings is 148px on wide browsers, and up to 744px (!!!) on mobiles. No wonder if your thumbnails are blurry then, right? 
So, increase the thumbnail size in the system main configuration. You might still run into trouble on some mobile screens, but unless you want to set thumbnail sizes of 744px minimum (your originally uploaded images are smaller than that!), you'd need to customize CSS.
The next "problem" is obvious: on product pages you've also set the image size to 100x100px. Review and change that too while you're at it. 
www.hikashop.com/support/support/documen...fig.html#main_images