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 $61.81   10.309%   $68.182   $68.18   $68.20   $68.20  
  Purchase #2 $44.56   6.552%   $47.4796   $47.48   $47.50   $47.50  
  Purchase #3 $50.25   12.323%   $56.4423   $56.44   $56.45   $56.40  
  Purchase #4 $163.66   6.340%   $174.036   $174.04   $174.05   $174.00  
  Purchase #5 $155.78   13.667%   $177.0705   $177.07   $177.05   $177.10  
  Purchase #6 $218.33   3.785%   $226.5938   $226.59   $226.60   $226.60  
  Purchase #7 $61.92   8.475%   $67.1677   $67.17   $67.15   $67.20  
  7 purchase totals = $756.31       $816.9719   $816.97   $817.00   $817.00