In asking this question, I assume that by "Bible" we mean the original penned documents at the hands of the authors themselves.  This is important because biblical copyists have made mistakes in the transmission of the biblical record (but it must be noted that such mistakes are extraordinarily minor such as one passage saying "Christ Jesus" instead of "Jesus Christ" or the inclusion of additional verse material not found in the most reliable manuscripts - i.e., 1 John 5:7).

Let me answer this in terms of tactic toward non-believers and in terms of whether or not the charge is true.  If a non-believer raises such a query about the Bible, you may want to reply by asking, "Would you then become a Christian if these alleged contradictions were satisfactorily explained to you?"  Presumably the answer would be a resounding "No."  Therefore, the charge of blblical errancy is a red herring to your discussion.  So I would say that one could address each of these questionable discrepancies after the weightier matters are addressed: Does God exist? Did Jesus rise again from the dead? etc ...

In terms of whether the initial charge is actually true will differ depending on which Christians you talk to.  Some, like Dale Tuggy, assert that the Bible contains errors but that they do not affect the core of the Gospel and overall message.  This is certainly a permissible stand to take.  But I have found that the alleged contradictions are nothing more than apparent - that is, that though they appear to be mutually exclusive, at the end of the day there are formidable answers that serve to dissolve the contradiction.  Literary scholars testify that it is very difficult to charge a historical document with being self-contradictory so the burden of proof will inevitably fall on the advocate of biblical errors.  But more often than not such alleged contradictions are the result of parroting other critics with an uninformed investigation on the matter.  For a good resource, I recommend the following if you are interested in surveying some of these discrepancies and how biblical conservatives address the problems therein: