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 $239.50   8.678%   $260.2838   $260.28   $260.30   $260.30  
  Purchase #2 $162.69   10.771%   $180.2133   $180.21   $180.20   $180.20  
  Purchase #3 $132.46   6.246%   $140.7335   $140.73   $140.75   $140.70  
  Purchase #4 $175.99   5.547%   $185.7522   $185.75   $185.75   $185.80  
  Purchase #5 $103.71   13.655%   $117.8716   $117.87   $117.85   $117.90  
  Purchase #6 $209.46   5.105%   $220.1529   $220.15   $220.15   $220.20  
  Purchase #7 $237.45   5.572%   $250.6807   $250.68   $250.70   $250.70  
  7 purchase totals = $1,261.26       $1,355.6880   $1,355.67   $1,355.70   $1,355.80