Proper way to Format text related to Functions in an Article about a Computer Package
First, as I argued in this answer, I suggest you to not use directly the command \texttt but to define a new command reflecting its purpose.

About your specific question, a common way is as follows:


Don't put parentheses if you are declaring the existence of a certain function  or making a reference to it (example from the Matlab documentation): 



  The inv function and the expression A^-1 both compute the matrix inverse.



Use the parentheses with the input argument list  when you want to describe the details of the function and its calling syntax:



  The function max(a,b) finds the maximum between the variables a and b.