1//gulp-sass will meet your request. Pls let me show you how to compile Sass files and minify (or compress) compiled css files:
2
3//install gulp-sass from here
4//in you project's gulpfile.js, add following code:
5//Note: outputStyle in gulp-sass has four options: nested, expanded, compact, compressed
6
7//It really works, I have used it in my project. Hope it helps.
8
9var gulp = require('gulp');
10var sass = require('gulp-sass');
11
12//sass
13gulp.task('sass', function () {
14    gulp.src(['yourCSSFolder/*.scss', 'yourCSSFolder/**/*.scss'])
15        .pipe(sass({outputStyle: 'compressed'}))
16        .pipe(gulp.dest('yourCSSFolder/'));
17});
18
19// Default task
20gulp.task('default', function () {
21    gulp.start('sass');
22});