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 $48.30   10.610%   $53.4246   $53.42   $53.40   $53.40  
  Purchase #2 $237.75   13.312%   $269.3993   $269.40   $269.40   $269.40  
  Purchase #3 $166.57   12.644%   $187.6311   $187.63   $187.65   $187.60  
  Purchase #4 $206.54   3.609%   $213.994   $213.99   $214.00   $214.00  
  Purchase #5 $152.68   12.831%   $172.2704   $172.27   $172.25   $172.30  
  Purchase #6 $33.83   6.280%   $35.9545   $35.95   $35.95   $36.00  
  Purchase #7 $52.32   5.622%   $55.2614   $55.26   $55.25   $55.30  
  7 purchase totals = $897.99       $987.9353   $987.92   $987.90   $988.00