http://ayende.com/blog/108545/the-tax-calculation-challenge?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+AyendeRahien+%28Ayende+%40+Rahien%29

taxes.js

var i,l,death,                                                                         
    taxes = [                                                                          
        {                                                                              
            value: 0,                                                                  
            rate: .1                                                                   
        },                                                                             
        {                                                                              
            value: 5070,                                                               
            rate: .14                                                                  
        },                                                                             
        {                                                                              
            value: 8660,                                                               
            rate: .23                                                                  
        },                                                                             
        {                                                                              
            value: 14070,                                                              
            rate: .30                                                                  
        },                                                                             
        {                                                                              
            value: 21240,                                                              
            rate: .33                                                                  
        },                                                                             
        {                                                                              
            value: 40230,                                                              
            rate: .45                                                                  
        }                                                                              
    ];                                                                                 
//Copy of args                                                                         
var args = process.argv.slice( 2 ), result = [];                                       
                                                                                       
for( i = 0, l = args.length; death = taxes.length, i < l; i ++ ){                      
                                                                                       
    args[ i ] = parseInt( args[ i ], 10 );                                             
    result[ i ] = 0;                                                                   
                                                                                       
    while( death-- > 0 ){                                                              
                                                                                       
        if( args[ i ] > taxes[ death ].value ){                                        
                                                                                       
            result[ i ] += ( args[ i ] - taxes[ death ].value )                        
                * taxes[ death ].rate;                                                 
            args[ i ] -= ( args[ i ] - taxes[ death ].value ); 
        }                                                                              
    }                                                                                  
    result[ i ] = Math.round( result[ i ] * 100 ) / 100;                               
    console.log( process.argv[ i + 2 ], 
                 '->', result[ i ] );                                                                                          
}