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 $215.93   13.226%   $244.4889   $244.49   $244.50   $244.50  
  Purchase #2 $53.37   10.824%   $59.1468   $59.15   $59.15   $59.10  
  Purchase #3 $131.67   7.116%   $141.0396   $141.04   $141.05   $141.00  
  Purchase #4 $159.53   5.560%   $168.3999   $168.40   $168.40   $168.40  
  Purchase #5 $129.71   7.829%   $139.865   $139.87   $139.85   $139.90  
  Purchase #6 $8.36   13.556%   $9.4933   $9.49   $9.50   $9.50  
  Purchase #7 $60.50   9.703%   $66.3703   $66.37   $66.35   $66.40  
  7 purchase totals = $759.07       $828.8038   $828.81   $828.80   $828.80