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 $40.56   7.330%   $43.533   $43.53   $43.55   $43.50  
  Purchase #2 $163.88   3.450%   $169.5339   $169.53   $169.55   $169.50  
  Purchase #3 $11.26   13.665%   $12.7987   $12.80   $12.80   $12.80  
  Purchase #4 $225.25   5.389%   $237.3887   $237.39   $237.40   $237.40  
  Purchase #5 $50.35   6.262%   $53.5029   $53.50   $53.50   $53.50  
  Purchase #6 $68.46   4.282%   $71.3915   $71.39   $71.40   $71.40  
  Purchase #7 $130.70   13.797%   $148.7327   $148.73   $148.75   $148.70  
  7 purchase totals = $690.46       $736.8814   $736.87   $736.95   $736.80