What is a reasonable percentage salary increase for tenure and promotion
Data on faculty salaries is available from the AAUP survey:

http://chronicle.com/article/2013-14-AAUP-Faculty-Salary/145679/#id=table

Associate professors make, very roughly speaking, 10% more than assistant professors.  However, since professors get a few percent raise a year, you can estimate that the difference between the most experienced assistant professor and the least experienced associate professor is about the typical annual raise.  So, I think the answer is "not much."  However, it varies widely by institution, school, department, governance model, etc.