If you have 10,000 employees that's $100M per year in expenses. If you're just renting payroll, purchasing, etc software for that price it'd be far cheaper to roll your own, or pay a few people to work on OSS full time.
This is the kind of hubris I come to this site for.
https://en.wikipedia.org/wiki/Chrysler_Comprehensive_Compens...
Payroll is harder than it looks due to all the edge cases. For example, it is literally possible for an employee to have so many payroll deductions including court-ordered wage garnishment that net pay would be negative. How do you handle that in all legal jurisdictions where the company operates?
By issuing a error and demanding that a human deal with it. Obviously.
If you mean it's impractical and error-prone to do payroll manually, well that's the point of automating >99.999% of it. For the remaining <0.001%, someone is going to have decide how to deal with it, and I'm sceptical that a programmer seven years ago will know better than a lawyer today what the legal requirements today are.
You could argue that payroll shouldn't be so complex but that's the reality of it today.
Second month was a disaster in the end they had to physically cut the tape on the last remaining partially destroyed copy - about 20% got paid on time.