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 $227.62   8.383%   $246.7014   $246.70   $246.70   $246.70  
  Purchase #2 $141.94   13.112%   $160.5512   $160.55   $160.55   $160.60  
  Purchase #3 $203.47   5.555%   $214.7728   $214.77   $214.75   $214.80  
  Purchase #4 $242.39   6.131%   $257.2509   $257.25   $257.25   $257.30  
  Purchase #5 $229.36   10.635%   $253.7524   $253.75   $253.75   $253.80  
  Purchase #6 $158.99   5.776%   $168.1733   $168.17   $168.15   $168.20  
  Purchase #7 $83.73   8.339%   $90.7122   $90.71   $90.70   $90.70  
  7 purchase totals = $1,287.50       $1,391.9142   $1,391.90   $1,391.85   $1,392.10