How to over write inc/template-tags.php in my child theme?

I wouldn't do that - it can cause big problems for future updates when I add more functions in there and call those functions elsewhere (you'll get an undefined function fatal error).

Every function in that file is wrapped in a function_exists() function, which means you can copy the entire function (including the function_exists() part) and add it to your child theme/plugin and it will overwrite the core function.

That's definitely the way you should go about it :)

Thanks Tom, that worked perfectly!

You're welcome :)