Career Advice (Math Major): Industry or Academia
That sounds like a tough decision but I see no reason why your long terms plans need to be decided now. Keep your options open by enrolling in the graduate level classes that will help you academic applications AND find a summer internship in industry. 

Make your decision only after you have applied to grad school (see where you are accepted) and have a better feeling about what you might want to do in the private sector (go on lots of informational interviews).  It is easier to change paths (and leave a PhD program early for industry) than the other way around.

I say act as if you are planning on going to grad school but have a backup plan in case you find an industry job you really like or are not accepted at the grad school of your choice.

Good luck!