Sorry, to answer your question, <h> tags are semantics and mark when your document has a heading. You can use css to style the heading however you wish it to look, but there are other software programs that rely on your document being correctly, semantically, marked - like accessibility programs.
A paragraph that is styled using css classes does not convey any special meaning to those programs.
Code:
Instead of: Use:
<p class="booktitle"> <h1>
<p class="chaptertitle"> <h2>
<p class="normalparagraph"> <p>
<p class="scenebreak"> <hr/>