Then how much do grades affect your first time getting hired, especially for jobs that are not completely academic, but for which a certain college degree is still required?
Then it depends on your field, but if you are only going to be judged for your position based on your degree, it will matter (it's a 'somewhat' to 'entirely' range).
If, however, you do have non-academic things to draw on, even in that situation, you can get away with lower marks. For example, if you are a programmer and have taken part of open-source/google projects/etc, then you get away with lower grades. And if you have a long list of community service (notably in the arts), or are otherwise socially involved... that matters too. And if you supported trade organizations, etc. for the business community (or networked, etc.)... and so on.
But for the first job, it tends to matter. Especially if you are younger, as in just out of college.
Keep in mind that it's still only the first job. Once you have it, if you look for experience and CV padding, marks won't really matter again. Also, early on, don't turn down promotions in any way. Even dead ends
within a company tend to work out when you try to make lateral transfers elsewhere.
(I'm assuming you are asking because your marks are lower, not higher. If they are higher, try to command a high salary instead, setting a higher initial bar to work from.)