Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $250.76   4.431%   $261.8712   $261.87   $261.85   $261.90  
  Purchase #2 $215.98   12.504%   $242.9861   $242.99   $243.00   $243.00  
  Purchase #3 $127.43   4.784%   $133.5263   $133.53   $133.55   $133.50  
  Purchase #4 $70.41   12.522%   $79.2267   $79.23   $79.25   $79.20  
  Purchase #5 $35.46   10.139%   $39.0553   $39.06   $39.05   $39.10  
  Purchase #6 $209.43   4.242%   $218.314   $218.31   $218.30   $218.30  
  Purchase #7 $41.84   12.766%   $47.1813   $47.18   $47.20   $47.20  
  7 purchase totals = $951.31       $1,022.1609   $1,022.17   $1,022.20   $1,022.20