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 $59.92   13.563%   $68.0469   $68.05   $68.05   $68.00  
  Purchase #2 $158.37   9.326%   $173.1396   $173.14   $173.15   $173.10  
  Purchase #3 $146.56   10.773%   $162.3489   $162.35   $162.35   $162.30  
  Purchase #4 $64.37   11.791%   $71.9599   $71.96   $71.95   $72.00  
  Purchase #5 $66.46   6.754%   $70.9487   $70.95   $70.95   $70.90  
  Purchase #6 $11.89   13.248%   $13.4652   $13.47   $13.45   $13.50  
  Purchase #7 $207.98   12.573%   $234.1293   $234.13   $234.15   $234.10  
  7 purchase totals = $715.55       $794.0385   $794.05   $794.05   $793.90