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 $194.50   5.256%   $204.7229   $204.72   $204.70   $204.70  
  Purchase #2 $68.47   3.698%   $71.002   $71.00   $71.00   $71.00  
  Purchase #3 $250.63   11.119%   $278.4975   $278.50   $278.50   $278.50  
  Purchase #4 $97.78   10.726%   $108.2679   $108.27   $108.25   $108.30  
  Purchase #5 $34.42   3.517%   $35.6306   $35.63   $35.65   $35.60  
  Purchase #6 $56.79   5.507%   $59.9174   $59.92   $59.90   $59.90  
  Purchase #7 $44.40   5.146%   $46.6848   $46.68   $46.70   $46.70  
  7 purchase totals = $746.99       $804.7231   $804.72   $804.70   $804.70