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 $208.99   8.114%   $225.9474   $225.95   $225.95   $225.90  
  Purchase #2 $59.48   5.423%   $62.7056   $62.71   $62.70   $62.70  
  Purchase #3 $38.59   9.790%   $42.368   $42.37   $42.35   $42.40  
  Purchase #4 $65.54   8.484%   $71.1004   $71.10   $71.10   $71.10  
  Purchase #5 $132.43   3.399%   $136.9313   $136.93   $136.95   $136.90  
  Purchase #6 $54.35   10.724%   $60.1785   $60.18   $60.20   $60.20  
  Purchase #7 $86.95   12.357%   $97.6944   $97.69   $97.70   $97.70  
  7 purchase totals = $646.33       $696.9256   $696.93   $696.95   $696.90