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 $43.63   10.767%   $48.3276   $48.33   $48.35   $48.30  
  Purchase #2 $113.34   9.380%   $123.9713   $123.97   $123.95   $124.00  
  Purchase #3 $77.35   5.125%   $81.3142   $81.31   $81.30   $81.30  
  Purchase #4 $250.68   4.112%   $260.988   $260.99   $261.00   $261.00  
  Purchase #5 $172.79   10.107%   $190.2539   $190.25   $190.25   $190.30  
  Purchase #6 $89.55   5.175%   $94.1842   $94.18   $94.20   $94.20  
  Purchase #7 $86.82   11.553%   $96.8503   $96.85   $96.85   $96.90  
  7 purchase totals = $834.16       $895.8895   $895.88   $895.90   $896.00