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 $38.61   7.766%   $41.6085   $41.61   $41.60   $41.60  
  Purchase #2 $104.27   10.584%   $115.3059   $115.31   $115.30   $115.30  
  Purchase #3 $145.90   9.578%   $159.8743   $159.87   $159.85   $159.90  
  Purchase #4 $135.54   11.556%   $151.203   $151.20   $151.20   $151.20  
  Purchase #5 $98.66   13.577%   $112.0551   $112.06   $112.05   $112.10  
  Purchase #6 $214.86   13.524%   $243.9177   $243.92   $243.90   $243.90  
  Purchase #7 $158.63   4.807%   $166.2553   $166.26   $166.25   $166.30  
  7 purchase totals = $896.47       $990.2198   $990.23   $990.15   $990.30