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 $60.80   3.571%   $62.9712   $62.97   $62.95   $63.00  
  Purchase #2 $107.79   12.491%   $121.254   $121.25   $121.25   $121.30  
  Purchase #3 $113.63   11.313%   $126.485   $126.49   $126.50   $126.50  
  Purchase #4 $78.25   5.357%   $82.4419   $82.44   $82.45   $82.40  
  Purchase #5 $42.99   5.600%   $45.3974   $45.40   $45.40   $45.40  
  Purchase #6 $12.89   10.261%   $14.2126   $14.21   $14.20   $14.20  
  Purchase #7 $102.42   9.406%   $112.0536   $112.05   $112.05   $112.10  
  7 purchase totals = $518.77       $564.8157   $564.81   $564.80   $564.90