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 $44.59   9.467%   $48.8113   $48.81   $48.80   $48.80  
  Purchase #2 $132.53   10.732%   $146.7531   $146.75   $146.75   $146.80  
  Purchase #3 $137.89   5.563%   $145.5608   $145.56   $145.55   $145.60  
  Purchase #4 $244.85   10.212%   $269.8541   $269.85   $269.85   $269.90  
  Purchase #5 $119.58   5.347%   $125.9739   $125.97   $125.95   $126.00  
  Purchase #6 $76.86   7.610%   $82.709   $82.71   $82.70   $82.70  
  Purchase #7 $109.97   3.174%   $113.4604   $113.46   $113.45   $113.50  
  7 purchase totals = $866.27       $933.1226   $933.11   $933.05   $933.30