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 $108.54   4.681%   $113.6208   $113.62   $113.60   $113.60  
  Purchase #2 $173.36   11.263%   $192.8855   $192.89   $192.90   $192.90  
  Purchase #3 $50.83   10.399%   $56.1158   $56.12   $56.10   $56.10  
  Purchase #4 $69.94   6.620%   $74.57   $74.57   $74.55   $74.60  
  Purchase #5 $197.89   13.531%   $224.6665   $224.67   $224.65   $224.70  
  Purchase #6 $57.67   13.428%   $65.4139   $65.41   $65.40   $65.40  
  Purchase #7 $64.68   3.865%   $67.1799   $67.18   $67.20   $67.20  
  7 purchase totals = $722.91       $794.4524   $794.46   $794.40   $794.50