In my url i'm passing parameters like
www.myexample.com/sample.php?BusinessId=5
The 5 in this case is the primary key of the database table "business."
Should I hash the "5" or is it ok to tell the world the primary key id?
Are there any security issues I should worry about?
Thanks!

That should be fine depending on other, un-named aspects of your program. Hashing isn't necessary. Sanitizing your data, however, is necessary.

PHP Code:

$business_id = (int)$_GET['BusinessId']; 


But can't some hacker write a scrapper by incrementing the id's?
For loop from BusinessId 1...1000

Yes there is security issues. Try URL rewrite to hide it, you can hash it( but do you really need that! ask yourself), or you can check the id with a given range ... if you are displaying data based on that id.

Security is rarely achieved by obfuscation. Authenticate properly if you don't want people accessing a page. Hashing isn't the correct solution b/c then anybody who has the URL will be able to access it. Make them login if you don't want it public.