cool_nameYa but your second job depends on your first job, which depends on grades
so grades clearly do matter
Your first job doesn't even fully depend
on grades. Companies tend to use GPA as a filter by which to narrow the field of candidates to interview (e.g. "must have a least 3.X GPA to apply). After that, it comes down to how well you sell yourself in the interview. I worked in a competitive field and even then the top companies didn't give a shit about grades as long as they were high enough to qualify for an interview: 3.5 (which, let's face it, is unremarkable).
After your first job, your track record of learning new skills, generating value as an employee, and above all being able to convince them that you're a pleasant person to be around for 40+ hours a week are what matter most.
From what I've observed, a lot of the time when people don't get job offers they shift the burden of blame to something external like their GPA or the other candidate having "connections," when usually the reason they didn't get hired is because they lack communication skills.
Even if grades did somehow wholly determine your first job, at what point do you reasonably assign the proximate cause of your career path? Why stop at GPA? How about that time your shoes came untied and you missed the bus and arrived at your midterm 15 minutes late and didn't finish the last 2 questions and got a C+ and damaged your GPA? Uh, blame the shoes? See how ridiculous this is?