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 $246.71   8.839%   $268.5167   $268.52   $268.50   $268.50  
  Purchase #2 $98.30   6.511%   $104.7003   $104.70   $104.70   $104.70  
  Purchase #3 $81.44   13.229%   $92.2137   $92.21   $92.20   $92.20  
  Purchase #4 $27.45   6.166%   $29.1426   $29.14   $29.15   $29.10  
  Purchase #5 $214.38   11.567%   $239.1773   $239.18   $239.20   $239.20  
  Purchase #6 $95.27   3.105%   $98.2281   $98.23   $98.25   $98.20  
  Purchase #7 $95.46   6.784%   $101.936   $101.94   $101.95   $101.90  
  7 purchase totals = $859.01       $933.9147   $933.92   $933.95   $933.80