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 $61.48   5.526%   $64.8774   $64.88   $64.90   $64.90  
  Purchase #2 $166.69   10.788%   $184.6725   $184.67   $184.65   $184.70  
  Purchase #3 $55.74   3.716%   $57.8113   $57.81   $57.80   $57.80  
  Purchase #4 $229.40   3.643%   $237.757   $237.76   $237.75   $237.80  
  Purchase #5 $122.63   6.383%   $130.4575   $130.46   $130.45   $130.50  
  Purchase #6 $9.54   3.685%   $9.8915   $9.89   $9.90   $9.90  
  Purchase #7 $246.99   4.386%   $257.823   $257.82   $257.80   $257.80  
  7 purchase totals = $892.47       $943.2902   $943.29   $943.25   $943.40