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 $56.98   10.358%   $62.882   $62.88   $62.90   $62.90  
  Purchase #2 $52.59   13.395%   $59.6344   $59.63   $59.65   $59.60  
  Purchase #3 $28.29   13.680%   $32.1601   $32.16   $32.15   $32.20  
  Purchase #4 $64.83   11.667%   $72.3937   $72.39   $72.40   $72.40  
  Purchase #5 $133.27   4.366%   $139.0886   $139.09   $139.10   $139.10  
  Purchase #6 $221.62   4.295%   $231.1386   $231.14   $231.15   $231.10  
  Purchase #7 $60.39   4.269%   $62.968   $62.97   $62.95   $63.00  
  7 purchase totals = $617.97       $660.2654   $660.26   $660.30   $660.30