Here's a hint. When trying to get your leg over the top tube of the frame, lean the bike. As your flexibility gets better, you'll need to lean it less and less. That's what I have to do with short legs.
Also, you should road test a bike before you purchase it, to make sure that it is the right fit. If the LBS won't let you road test it, then go to another LBS.
Also, inseam is as important as your total height in getting a bike that fits.
Here's a chart that will get you close on the right bike size. But since every manufacturer uses a slightly different geometry, different bikes will feel differently to you. The top tube is not the same length on every bike of the same size, and that will affect your comfort level.
Since you're new and you want a road bike (with drop bars I'm assuming), you'll probably want a road bike with an endurance geometry. But try a few bikes that fit you with different geometries to see which you like best.
GH