Alot of good advice here, pretty much just pick apart anything she says. Your problem is, and i do the same thing too, as im sure the rest of us. We kind of plan the next thing we are about to say as she is answering your conversation starter. Like if you started conversation with " woah...I've never seen such a long line.." she is gonna say some 8 word reply,like "ya i know, i heard the other cashier was robbed" and within milliseconds your probably thinking of what your gonna say next, it'll probably be something about her response. After like the 4th response, the conversation is bound to fall flat, or sound really dull. Instead pick apart her sentences and put your mind "OUT THERE" and not in the driver's seat. Listen really careful to her sentences, for example, when she said robbery "you could probably say, "a robbery? i hope you didnt have nothing to do with it, because i'll call batman." ( i know bad example, but i hope u see the point)
and if you get mall reply like the other guy said^ i wouldnt even ask what mall you went to, as for me, she'll give a one word reply, and make convo real dull, instead maybe say, "ya, how much did you spend, you look like you have a spending habbit" (you kinda just wanna stray from short answers from her, as i think its some people's natural response, for them to give you a short reply, so they can stop talking about themselves, and have you do all the talking) What helps, is imagine the sentences that she's saying, being written in your head, and as the sentences run through your head, pick apart the nouns and verbs, and continue conversation off of thoose.