Most companies these days have people responsible for external innovation and business developement. Somebody with the tittle 'licensing' might also be appropriate. But the key is - never try talking to R&D or marketing people and make sure you have a solid value proposition to offer.
Some times companies have an official portal or form you could submit for their review. If not, using professional intermediary is a better way than to knock the front door.

This is an incredibly narrow niche you've picked.

I suggest you went at this the wrong way around. Contact companies you believe you can do something for and get THEM to buy in on software that you develop for them...get the customers BEFORE you start programming.

It'll save you a lot of difficulty and frustration.

You can use the Little Unsure technique with receptionists to get into the company. Then repeat it with whoever answers (the receptionist may get it wrong).

http://www.salestactics.org/how-to-get-to-the-decision-maker/

As high as possible, but at a minimum, contact someone whose compensation is at least partly based on online sales, because that's the factor you'll be most likely to influence. Titles will vary by company, but depending on the company, it could be the VP of Marketing, VP of Online Marketing, etc.

To eliminate guesswork, several of my portfolio companies have had great results by contacting the CEO's office (you'll get their assistant usually), with something like: "I have a visualization technology that can help your company increase online sales, who would be the best person to contact." Now you're 1) getting to the right person, and 2) coming from the CEO's office, so they can't blow you off.

If you haven't already, also consider how you can build up an intellectual property "fence" around your technology by filing for copyrights, trademarks and patents, as appropriate. This will help you minimize competitors down the road if you're successful, and also increase the enterprise value of your business in the event you ever want to sell it.

Book a call to get more detailed strategies on how to sell larger companies as a small startup and ways to protect your idea from vultures (both customers and competitors).