Say I want to get a master's degree at a university, and a requirement is to have a 3.0 gpa in the last 90 credit hours.
If I just complete my undergraduate BS with a 2.7 gpa, would I be able to take classes at my local community college in order to boost my "recent" gpa to a 3.0, submit my transcripts from my BS college and the community college, and be acknowledge as having a 3.0 in the last 90 credit hours?

Yes you could but you may also consult an advisor some programs will allow students in on a conditional basis where you may have conditions like no C's or you may substitute the gpa portion of the requirement for a sufficient score on a test like Gmat

Consult an advisor before wasting your time at a cc to boost your gpa that small amount

You don't need to assume or take anyone's assumption on d2jsp
Talk to the department, every single one have different policies and they will be able to work with you as long as you do your part.
having a low gpa doesn't mean you'll never be able to get a masters, it just means it might take you longer to get started

the only advice you should follow

This is pretty key.

If you're trying to raise your GPA one of your best options is to re-take any classes you got low grades in to raise your GPA. If you have a couple of C's or F's that are on your transcript then those will bring down your GPA, re-taking those and bringing up the grade to a B perhaps may help to raise your GPA overall. However, your cumulative GPA and your overall GPA from your degree may vary depending on these grades. Contact your academic adviser from your current school to see along with the one from your proposed graduate school.