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 $97.50   8.323%   $105.6149   $105.61   $105.60   $105.60  
  Purchase #2 $37.68   11.334%   $41.9507   $41.95   $41.95   $42.00  
  Purchase #3 $57.72   5.137%   $60.6851   $60.69   $60.70   $60.70  
  Purchase #4 $245.25   6.375%   $260.8847   $260.88   $260.90   $260.90  
  Purchase #5 $114.72   8.746%   $124.7534   $124.75   $124.75   $124.80  
  Purchase #6 $104.71   9.725%   $114.893   $114.89   $114.90   $114.90  
  Purchase #7 $76.99   9.291%   $84.1431   $84.14   $84.15   $84.10  
  7 purchase totals = $734.57       $792.9249   $792.91   $792.95   $793.00