DO NOT USE TABS IN YOUR E-BOOK DOCUMENTS.
I say that as a copy editor pursuant to 16CMS 2.77(7).
And I say that as a CP to a professional formatter. Manual tabs make additional problems in that context.
Simply use MSWord's Page Setup or Page Layout (depending upon whether your edition is 2007 or 2010, respectively) or use the Paragraph menu or fix the indent on the Ruler as you wish. A quick Internet search will help you with any of those options if needed.
Denise Barker, author + blogger + copy editor