Outbound links are not considered in Google rankings. However, outbound links to quality sites add to your visitors' experience and you should use them. Outbound links contribute to the online community, and are considered good practice.
If for some reason you are concerned that someone will leave your website, simply insert code that allows a tab to pop-up. This will ensure your website still remains on the users tabs and makes it much more likely that they will come back and continue to browse your site.