Not as much as many would have you believe, though aiming for A/B grades in your core curricula would be a good thing generally. In many colleges with grade inflation (and this particularly includes more selective schools), anything less than a 'B' is pretty much the mark of death. In engineering or STEM programs, it's not unusual for the median grade in and early "weeder" course to be a D or F.
In many cases, what a high GPA shows is that you've got a highly developed ability to get along with the system. For positions in which that's important, you'll get higher consideration than someone with a lower GPA.
There are a lot of observations about how grades don't correlate well with innate ability. There are several well-known cases of highly successful tech entrepreneurs who'd dropped out of college (Jobs, Gates, Zuckerberg). Though I can also think of many who've completed undergrad or advanced-degree programs as well. Robert Pirsig in Zen and the Art of Motorcycle Maintenance notes that his best students (he was a college professor for a time) got the worst grades. Of course, the worst students did as well, so don't be guided by false equivalence. My experience is that if you're actively and directly questioning material, you may well find your nominal academic performance suffers for it.
For tech in particular, execution matters far more than GPA, and having a solid project or projects under your belt will amount for far more than a high GPA. I know and have worked with many people who lack a formal college degree but who were absolutely brilliant in their work. Sadly, the lack of degree can limit opportunities and/or upward mobility in many firms, though this may change, particularly with recent trends in college costs and financing.