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 $93.46   11.554%   $104.2584   $104.26   $104.25   $104.30  
  Purchase #2 $26.43   8.407%   $28.652   $28.65   $28.65   $28.70  
  Purchase #3 $164.95   12.104%   $184.9155   $184.92   $184.90   $184.90  
  Purchase #4 $136.42   8.862%   $148.5095   $148.51   $148.50   $148.50  
  Purchase #5 $236.57   12.655%   $266.5079   $266.51   $266.50   $266.50  
  Purchase #6 $163.33   10.448%   $180.3947   $180.39   $180.40   $180.40  
  Purchase #7 $96.43   5.450%   $101.6854   $101.69   $101.70   $101.70  
  7 purchase totals = $917.59       $1,014.9234   $1,014.93   $1,014.90   $1,015.00