Business & farm

Must the expense cover an auto or business asset to be ordinary or necessary?

 

In my case, cycle time to get to my tenant matters because it is necessary. I explained my real life examples in this post. Solved: Re: How to deduct Roadside Assistance premium? (intuit.com)

How does one get a definitive ruling/opinion from the IRS on the this expense? Or is it left to the tax filer?