Yes, this is fine. But, you will have to spin the brush out every time you want to use it again. I think the better option is to wrap the brush in plastic so that no air is getting to the bristles and it will not dry out that way.

Yes, you can keep it in water, as to not let it dry up, while you are working. But, when you need the brush again, you will need to get rid of the water, or you will have a drippy mess. With this method, you will basically end up having to rinse before using again. I think the store guy meant to soak it in water once you are done with it, that way you don't have to wash it right away.

If I need to put my brush down for a few minutes, I use my paint to keep it moist. Simply wet it (or dip it) with the paint and put it down on a flat surface so the paint doesn't drain off (either rest it across the paint can or the paint tray or even the paint can lid).

However, you should always wash your brushes (soap and water) when you are done with them to keep them healthy and lasting longer. There are brush cleaners, but if you take care to wash the brush thoroughly after each use, you will never need those.

I don't do this with basic wall painting (or contract painting), but when I am doing artwork, I put a drop of dishwashing liquid in the water and it keeps the bristles soft. The cost of artist's brushes are crazy!

Since this post, I read why it's not a good idea to not to keep a paintbrush immersed in water overnight. I did clean the brush and wrapped it in plastic. Also, this project will take at least a few days-I read that a painter doesn't clean the brush while working on a project-he just wraps it in plastic until he is done with the project-what do you think about this? Also, once I am done with this project after I clean it, should I let it dry and store it in a plastic bag or saran wrap?

Thanks again,
Karen

Once it's cleaned, you do not need to store it in plastic. That's only if you are using it and it's full of paint.
You can lay the clean brush flat, or standing in a cup bristle side up. Never leave your brushes resting on the bristles.
I personally don't leave my brushes wrapped overnight. I take the few minutes to clean them while I am washing my hands. The roller, on the other hand, I do wrap air-tight in plastic and put in the refridgerator. And, leave paint on the roller, it stays nice and moist for work the next day.

I like to hang my brushes bristles-down from pegboard hooks. The bristles stay nice and straight, and dry quickly.

Get a brush comb, too. It's got a row of sharp metal pins that you can comb the bristles with while rinsing the brush, it speeds up the process and doesn't allow bristles to cross or tangle. In the store they should be sold very near where the paint brushes are.