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 $64.55   7.818%   $69.5965   $69.60   $69.60   $69.60  
  Purchase #2 $51.39   12.230%   $57.675   $57.68   $57.70   $57.70  
  Purchase #3 $6.46   3.823%   $6.707   $6.71   $6.70   $6.70  
  Purchase #4 $237.35   12.334%   $266.6247   $266.62   $266.60   $266.60  
  Purchase #5 $62.90   9.207%   $68.6912   $68.69   $68.70   $68.70  
  Purchase #6 $144.48   9.788%   $158.6217   $158.62   $158.60   $158.60  
  Purchase #7 $159.46   4.212%   $166.1765   $166.18   $166.20   $166.20  
  7 purchase totals = $726.59       $794.0926   $794.10   $794.10   $794.10