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 $48.83   5.434%   $51.4834   $51.48   $51.50   $51.50  
  Purchase #2 $122.36   6.758%   $130.6291   $130.63   $130.65   $130.60  
  Purchase #3 $17.45   4.716%   $18.2729   $18.27   $18.25   $18.30  
  Purchase #4 $73.68   13.232%   $83.4293   $83.43   $83.45   $83.40  
  Purchase #5 $200.75   3.287%   $207.3487   $207.35   $207.35   $207.30  
  Purchase #6 $230.71   13.269%   $261.3229   $261.32   $261.30   $261.30  
  Purchase #7 $241.65   7.205%   $259.0609   $259.06   $259.05   $259.10  
  7 purchase totals = $935.43       $1,011.5472   $1,011.54   $1,011.55   $1,011.50