Usually people have different preferences on tabs vs spaces. Here is a git filter to convert tabs to spaces, and spaces to tabs. Git allows you to write filters - a small commands which will be run after checkout (smudge) or before add (clean). As usual all settings are stored in git config files.

To make a work I use two GNU tools expand (converts tabs to spaces) and unexpand (converts spaces to tabs). If you are using Windows, then you'll need these tools to be reachable from your PATH environment varible. You can get this tools as part of GnuWin32 or any other port of GNU tools to Windows.

DISCLAMER: Be really careful before commiting, as these filters can produce a huge changesets.

Tabify - spaces to tabs on add

1. Open your ~/.gitconfig (%SystemDrive%\Users\<username>\.gitconfig in case of Windows)
2. Add following lines

[filter "tabify"]
    clean = unexpand --tabs=4 --first-only

It says that we want to convert each 4 space characters at the beginning of a line to one tab.

1. To make the filter active add following lines to your .gitconfig (or to .git\info\attributes)

*.cs filter=tabify

It says that for files with ".cs" extension we want to use this filter.

Spacify - spaces to tabs on add

1. Open your ~/.gitconfig (%SystemDrive%\Users<username>.gitconfig in case of Windows)
2. Add following lines

[filter "spacify"]
    clean = expand --tabs=4 --initial

It says that we want to convert each tab character at the beginning of line to 4 space characters.

1. To make the filter active add following lines to your .gitconfig (or to .git\info\attributes)

*.cs filter=spacify

It says that for files with ".cs" extension we want to use this filter.

Spaces2Tabs - spaces to tabs on add, and tabs to spaces on checkout.

This filter is just a combination of previous two filters. This filter is usefull if your repository requires you to use tabs for indents, but you prefer spaces. The code

[filter "spaces2tabs"]
    clean = unexpand --tabs=4 --first-only
    smudge = expand --tabs=4 --initial  

Tabs2Spaces - tabs to spaces on add, and spaces to tabs on checkout.

This filter is just a combination of first two filters. This filter is usefull if your repository requires you to use spaces for indents, but you prefer tabs. The code

[filter "tabs2spaces"]
    clean = expand --tabs=4 --initial
    smudge = unexpand --tabs=4 --first-only

Happy filtering!