There was a tag proposed for HTML 3.0, but it was never adopted by any major browser and the draft specification has now expired. You can simulate a tab or indent in various ways, including using a transparent GIF, but none are quite as satisfactory or widely supported as an official tag would be.
My page looks good on one browser, but not on another.
There are slight differences between browsers, such as Netscape Navigator and Microsoft Internet Explorer, in areas such as page margins. The only real answer is to use standard HTML tags whenever possible, and view your pages in multiple browsers to see how they look.