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 $186.54   9.199%   $203.6998   $203.70   $203.70   $203.70  
  Purchase #2 $11.35   8.533%   $12.3185   $12.32   $12.30   $12.30  
  Purchase #3 $123.88   7.285%   $132.9047   $132.90   $132.90   $132.90  
  Purchase #4 $161.37   10.368%   $178.1008   $178.10   $178.10   $178.10  
  Purchase #5 $242.73   4.271%   $253.097   $253.10   $253.10   $253.10  
  Purchase #6 $20.81   6.181%   $22.0963   $22.10   $22.10   $22.10  
  Purchase #7 $47.53   12.337%   $53.3938   $53.39   $53.40   $53.40  
  7 purchase totals = $794.21       $855.6109   $855.61   $855.60   $855.60