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 $113.82   4.271%   $118.6813   $118.68   $118.70   $118.70  
  Purchase #2 $177.34   9.747%   $194.6253   $194.63   $194.65   $194.60  
  Purchase #3 $205.66   7.407%   $220.8932   $220.89   $220.90   $220.90  
  Purchase #4 $130.34   11.453%   $145.2678   $145.27   $145.25   $145.30  
  Purchase #5 $187.43   13.552%   $212.8305   $212.83   $212.85   $212.80  
  Purchase #6 $237.40   12.233%   $266.4411   $266.44   $266.45   $266.40  
  Purchase #7 $236.55   10.641%   $261.7213   $261.72   $261.70   $261.70  
  7 purchase totals = $1,288.54       $1,420.4605   $1,420.46   $1,420.50   $1,420.40