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 $179.60   13.457%   $203.7688   $203.77   $203.75   $203.80  
  Purchase #2 $173.95   12.227%   $195.2189   $195.22   $195.20   $195.20  
  Purchase #3 $194.58   7.273%   $208.7318   $208.73   $208.75   $208.70  
  Purchase #4 $119.43   10.687%   $132.1935   $132.19   $132.20   $132.20  
  Purchase #5 $32.35   8.628%   $35.1412   $35.14   $35.15   $35.10  
  Purchase #6 $72.66   13.837%   $82.714   $82.71   $82.70   $82.70  
  Purchase #7 $122.95   13.266%   $139.2605   $139.26   $139.25   $139.30  
  7 purchase totals = $895.52       $997.0287   $997.02   $997.00   $997.00