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 $246.58   8.806%   $268.2938   $268.29   $268.30   $268.30  
  Purchase #2 $70.35   9.257%   $76.8623   $76.86   $76.85   $76.90  
  Purchase #3 $66.27   11.509%   $73.897   $73.90   $73.90   $73.90  
  Purchase #4 $199.61   4.588%   $208.7681   $208.77   $208.75   $208.80  
  Purchase #5 $132.70   7.339%   $142.4389   $142.44   $142.45   $142.40  
  Purchase #6 $18.97   10.384%   $20.9398   $20.94   $20.95   $20.90  
  Purchase #7 $167.82   8.709%   $182.4354   $182.44   $182.45   $182.40  
  7 purchase totals = $902.30       $973.6353   $973.64   $973.65   $973.60