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 $66.44   9.223%   $72.5678   $72.57   $72.55   $72.60  
  Purchase #2 $90.61   9.410%   $99.1364   $99.14   $99.15   $99.10  
  Purchase #3 $97.68   3.397%   $100.9982   $101.00   $101.00   $101.00  
  Purchase #4 $101.83   5.688%   $107.6221   $107.62   $107.60   $107.60  
  Purchase #5 $136.66   12.277%   $153.4377   $153.44   $153.45   $153.40  
  Purchase #6 $10.29   6.356%   $10.944   $10.94   $10.95   $10.90  
  Purchase #7 $35.51   9.626%   $38.9282   $38.93   $38.95   $38.90  
  7 purchase totals = $539.02       $583.6344   $583.64   $583.65   $583.50