If what you want is to browse local HTML5 files on the iPad, your options are limited. The only app I know of that will do this is HTML Presenter. You have to zip the site/files and place them in DropBox to download to the app. It's not perfect, but will handle basic pages fairly well.
There are probably other apps for this, but the need to download the file(s) into the app by some method or point the app at a cloud service is probably going to be universal. The iPad does not have a common file space/folder accessible to all apps, so you can't just download files and point an app at them.
If you are looking to edit HTML files on the iPad, there are several apps for that, usually with their own built in browsers to view the results. I have no recommendations for actual apps. Just search the App Store for HTML editor.