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 $59.88   5.273%   $63.0375   $63.04   $63.05   $63.00  
  Purchase #2 $44.50   3.254%   $45.948   $45.95   $45.95   $45.90  
  Purchase #3 $250.39   4.235%   $260.994   $260.99   $261.00   $261.00  
  Purchase #4 $132.38   6.628%   $141.1541   $141.15   $141.15   $141.20  
  Purchase #5 $150.93   7.615%   $162.4233   $162.42   $162.40   $162.40  
  Purchase #6 $63.39   4.227%   $66.0695   $66.07   $66.05   $66.10  
  Purchase #7 $63.70   8.208%   $68.9285   $68.93   $68.95   $68.90  
  7 purchase totals = $765.17       $808.5549   $808.55   $808.55   $808.50