That looks technically correct as long as the character string "tagid" doesn't appear in any other URLs except the ones you want to disallow crawling for. If you say "Disallow: /*?tagid" then including the "?" would limit the rule to just query string parameters - that might be even safer.
Another step you can take is to use your Webmaster Tools account to tell Google to ignore the "tagid" parameter. Look under the Configuration > URL Parameters section.