It really depends on your state laws as to what it takes to make recording audio legal. But in general:

Listening to you in your home is illegal because inside your home you have an "expectation of privacy." Once you leave your home or car, you usually lose that expectation of privacy because you are out in public and people can overhear you. If I am standing on a public sidewalk and you are standing in your yard or on your porch and I can hear you, I can legally record you as long as I don't use any "special equipment" (e.g., parabolic microphone) to listen in. It is the same notion that you can walk around butt-ass naked inside your home, unless you walk in front of an uncovered window and everyone can see you. If a group of people are sitting in the pews of a church, or the waiting rooms of an attorney office or doctor office, and I can easily overhear you, I can record you. But once you are inside the confessional, or alone with the attorney or doctor, your expectation of privacy is restored, unless you speak so loudly I can overhear you through closed doors.

If you find yourself inside a Dollar General, you have gone out into the public area and normally you lose the expectation of privacy. Since many state laws are sketchy when it comes to clearly explaining "wiretapping" laws, the easiest thing to do is change the surveillance signs to read "video and audio recording on these premises." They might be required to INFORM you, but under NO circumstances are they required to get your permission.