I think you should try grunt-contrib-sass that have internal support for compass:
https://npmjs.org/package/grunt-contrib-sass
from documentation:
compass
Type: Boolean
Default: false
Make Compass imports available and load project configuration
(config.rb located close to the Gruntfile.js).
And you can use global patterns of gruntjs:
http://gruntjs.com/configuring-tasks#globbing-patterns
sass: {
dist: {
files: [
{
src: 'app/styles/specific/**/*.scss',
dest:'.tmp/styles/specific.css'
},
{
src: ['app/styles/**/*.scss', '!app/styles/specific/**/*.scss'],
dest:'.tmp/styles/main.css'
}
]
}
}