I am also having the same issues with employees. The almost never ring up customers even when assigned to do so as a task. I have only had them do it one time after I sat there and waited for them to do it for a long time. Many sales are lost because of it because it takes so long to ring them up that my sim cannot do them all. The option to scold them for slacking is greyed out and it says they are not slacking (I think because all their talking is actually them performing the function of making sales).
I also think the process to restock and ring up takes too long although I haven't gotten the perk to speed it up yet so I can't say how much faster that is but will try it once I get more points saved up.
My temporary solution is to have more than one member of the household work in the store. You can then direct the sims you control to ring up the customers. At this point having employees is basically worthless.
Another observation is that when I visited the store as customer using another household items could be instantly purchased and there was no ringing up process. I also observed the employees tending to their duties much more diligently.
Firing does not help because no matter how high their work ethic skill is they still spend all day slacking off.
No mods, no CC.
Thanks