While you won't see any changes to your SERP positions or indexing regardless of which path you take here, you're doing the right thing by having internal links open in the same tab. (As @closetnoc pointed out above, including the attribute at all is a bit redundant, since the default behavior of links is to open in the same tab, unless otherwise specified.)
Conventionally, webmasters have chosen to open links leading to other websites in a different tab, and links that keep you on the same domain in the same tab. There could be business use cases for opening an internal link in a different tab; for example, event registration funnels or purchase flows. But it doesn't affect SEO, and there's nothing that needs to be adjusted in Google Analytics.