Most Some publishers use <p class="someclass">Chapter One</p> for the chapter title....
....and I would add that although it is certainly
possible to do it that way, I would recommend using the <h1-6> tags for their semantically correct purpose of providing a heading hierarchy. You can apply the exact same CSS to the <h> tags and visually it will be identical, but automated systems, accessibility systems, etc. can figure out the structure of your document much better/faster(/stronger??) if you use the proper markup.
It also has the added benefit of programs like Calibre or Sigil creating the automated ToC based on your <h> tags - as has been mentioned above.