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 $69.27   10.301%   $76.4055   $76.41   $76.40   $76.40  
  Purchase #2 $82.76   11.151%   $91.9886   $91.99   $92.00   $92.00  
  Purchase #3 $43.58   5.767%   $46.0933   $46.09   $46.10   $46.10  
  Purchase #4 $243.83   7.402%   $261.8783   $261.88   $261.90   $261.90  
  Purchase #5 $109.59   13.567%   $124.4581   $124.46   $124.45   $124.50  
  Purchase #6 $146.25   9.644%   $160.3544   $160.35   $160.35   $160.40  
  Purchase #7 $85.41   11.387%   $95.1356   $95.14   $95.15   $95.10  
  7 purchase totals = $780.69       $856.3138   $856.32   $856.35   $856.40