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 $63.99   13.425%   $72.5807   $72.58   $72.60   $72.60  
  Purchase #2 $83.54   13.758%   $95.0334   $95.03   $95.05   $95.00  
  Purchase #3 $236.81   6.366%   $251.8853   $251.89   $251.90   $251.90  
  Purchase #4 $221.27   8.286%   $239.6044   $239.60   $239.60   $239.60  
  Purchase #5 $68.67   7.373%   $73.733   $73.73   $73.75   $73.70  
  Purchase #6 $11.96   5.352%   $12.6001   $12.60   $12.60   $12.60  
  Purchase #7 $163.38   9.249%   $178.491   $178.49   $178.50   $178.50  
  7 purchase totals = $849.62       $923.9279   $923.92   $924.00   $923.90