Thank you! The Plugin suggested makes my pop-up Thickbox look awesome! I appreciate that tip. I also figured out that- for just the static thumbnails I can go into WordPress Admin, and select Gallery, then Styles and I was able to add an extra line of code to my Default Styles (so that all my galleries using this style automatically round/curves their corners) You can customize the radius px numbers
.ngg-gallery-thumbnail img {
background-color:#FFFFFF;
border:0px solid #A9A9A9;
display:block;
margin:4px 0px 4px 5px;
padding:0px;
position:relative;
-moz-border-radius:10px;-webkit-border-radius:10px;border-radius:10px;
}