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 $59.89   7.282%   $64.2512   $64.25   $64.25   $64.30  
  Purchase #2 $120.80   10.702%   $133.728   $133.73   $133.75   $133.70  
  Purchase #3 $62.81   3.266%   $64.8614   $64.86   $64.85   $64.90  
  Purchase #4 $231.95   5.319%   $244.2874   $244.29   $244.30   $244.30  
  Purchase #5 $118.68   10.553%   $131.2043   $131.20   $131.20   $131.20  
  Purchase #6 $27.43   12.227%   $30.7839   $30.78   $30.80   $30.80  
  Purchase #7 $249.60   6.750%   $266.448   $266.45   $266.45   $266.40  
  7 purchase totals = $871.16       $935.5642   $935.56   $935.60   $935.60