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 $241.75   4.859%   $253.4966   $253.50   $253.50   $253.50  
  Purchase #2 $53.28   12.554%   $59.9688   $59.97   $59.95   $60.00  
  Purchase #3 $236.76   5.767%   $250.4139   $250.41   $250.40   $250.40  
  Purchase #4 $58.43   3.836%   $60.6714   $60.67   $60.65   $60.70  
  Purchase #5 $46.62   9.150%   $50.8857   $50.89   $50.90   $50.90  
  Purchase #6 $231.98   6.316%   $246.6319   $246.63   $246.65   $246.60  
  Purchase #7 $120.45   8.134%   $130.2474   $130.25   $130.25   $130.20  
  7 purchase totals = $989.27       $1,052.3157   $1,052.32   $1,052.30   $1,052.30