Gruntfile2.js

module.exports = function(grunt) {

    // Project configuration.
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),

        // Watch
        watch: {
            options: {
                cwd: 'httpdocs/'
            },
            css: {
                files: ['src/scss/**/**/*.scss'],
                tasks: ['sass', 'autoprefixer', 'bs-reload'],
            },
            uglify: {
                files: ['src/js/**/*.js','!**/*.min.js'],
                tasks: ['uglify'],
            },
            concat: {
                files: ['src/js/**/*.js'],
                tasks: ['concat'],
            }
        },

        // AUTOPREFIXER
        autoprefixer: {
            options: {
                // Task-specific options go here.
                // browsers - https://github.com/ai/autoprefixer#browsers
                browsers: ['> 5%', 'last 2 version', 'ie 9']
            },
            // prefix all files
            no_dest_multiple: {
                src: 'httpdocs/static/css/*.css'
            }
        },

        // BROWSER SYNC - This not needed when using the API
        // https://www.npmjs.org/package/grunt-browser-sync
//        browserSync: {
//            dev: {
//                bsFiles: {
//                    src : [
//                        'httpdocs/static/css/*.css',
//                        'httpdocs/static/js/**/*.js',
//                        'httpdocs/**/*.html'
//                    ]
//                },
//                options: {
//                    watchTask: true,
//                    server: {
//                        baseDir: "httpdocs/"
//                    }
//                }
//            }
//        },

        // UGLIFY
        uglify: {
            build: {
                // src: ['src/js/**/*.js'],
                // dest: 'src/js/<%= pkg.name %>.min.js'
                // We're being quite explicit
                files: {
                    'httpdocs/src/js/dh-tabs.plugin.min.js': ['httpdocs/src/js/dh-tabs.plugin.js'],
                    'httpdocs/src/js/<%= pkg.name %>.min.js': ['httpdocs/src/js/<%= pkg.name %>.js'],
                }
            }
        },

        // CONCAT JS
        concat: {
            options: {
                separator: ';',
                banner: '/*! \nJS for <%= pkg.name %> - v<%= pkg.version %>\nAuthor: <%= pkg.author %>\nModified: <%= grunt.template.today("yyyy-mm-dd") %>\n */\n',
            },
            dist: {
                // src: ['src/**/*.js'],
                // dest: 'static/js/all.min.js'
                // We're explicit in what files/order we concat...
                src: ['httpdocs/src/js/dh-tabs.plugin.min.js','httpdocs/src/js/<%= pkg.name %>.min.js'],
                dest: 'httpdocs/static/js/app.min.js'
            }
        },

        // SASS
        sass: {
            dist: {
                options: {
                    style: 'compressed',
                    banner: '/*!\n@project: <%= pkg.name %> by <%= pkg.author %>\n@modified: <%= grunt.template.today("yyyy-mm-dd") %>\n*/\n'
                },
                files: {
                    'httpdocs/static/css/style.min.css':'httpdocs/src/scss/style.scss'
                }
            }
        }

    });

    // Start BrowserSync via the API
    var bs;
    grunt.registerTask("bs-start", function () {
        var browserSync = require("browser-sync");
        bs = browserSync.init([
            'httpdocs/static/js/**/*.js',
            'httpdocs/**/*.html'
        ], {
            server: {
                baseDir: "httpdocs/"
            }
        })
    });

    // Fire file-change events manually for greater control
    grunt.registerTask("bs-reload", function () {
        bs.events.emit("file:changed", {path: "style.css"});
        bs.events.emit("file:changed", {path: "style2.css"});
    });

        // Load the plugin that provides the "uglify" task.
    // grunt.loadNpmTasks('grunt-XXXX');
    require('load-grunt-tasks')(grunt);

    // Default task(s).
    grunt.registerTask('default', ['bs-start', 'watch']);

};

NOTE: you may need to run npm install browser-sync --save-dev before using this, not grunt-browser-sync!

This Gruntfile.js shows how you can use BrowserSync via the api for greater control.

You can see on line 14 we call a custom task AFTER all previous CSS tasks.

on lines 107-108 we watch other files as normal (ones that don't have multiple tasks assigned to them) and then provide config as normal.

Finally on line 127 we run browserSync followed by the watch task.

ooh, interesting - will try this. Thanks a lot @shakyShane!