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 $51.59   11.697%   $57.6245   $57.62   $57.60   $57.60  
  Purchase #2 $248.88   4.852%   $260.9557   $260.96   $260.95   $261.00  
  Purchase #3 $176.48   9.784%   $193.7468   $193.75   $193.75   $193.70  
  Purchase #4 $153.78   6.406%   $163.6311   $163.63   $163.65   $163.60  
  Purchase #5 $203.75   8.859%   $221.8002   $221.80   $221.80   $221.80  
  Purchase #6 $242.72   6.824%   $259.2832   $259.28   $259.30   $259.30  
  Purchase #7 $53.43   11.786%   $59.7273   $59.73   $59.75   $59.70  
  7 purchase totals = $1,130.63       $1,216.7688   $1,216.77   $1,216.80   $1,216.70