I see, sorry i missed the part that was CMS Builder.
you will need to edit the webassist/ckeditor/style_lists/stylelist1.js to add the table style.
for example, the last style defined in that file is:
{ name: "contentpage-clicked", element: "span", ordered_list: [ "a:0" ], attributes: { "class" : "contentpage-clicked" } }
you would need to add your style for the table tag after that like this:
{ name: "contentpage-clicked", element: "span", ordered_list: [ "a:0" ], attributes: { "class" : "contentpage-clicked" } },
{ name: "tableStyle", element: "table", ordered_list: [ "s:0" ], styles: { "border" : "1px solid black" } }