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 $241.99   5.212%   $254.6025   $254.60   $254.60   $254.60  
  Purchase #2 $57.53   4.414%   $60.0694   $60.07   $60.05   $60.10  
  Purchase #3 $235.48   10.820%   $260.9589   $260.96   $260.95   $261.00  
  Purchase #4 $239.80   10.611%   $265.2452   $265.25   $265.25   $265.20  
  Purchase #5 $130.59   4.533%   $136.5096   $136.51   $136.50   $136.50  
  Purchase #6 $121.28   12.318%   $136.2193   $136.22   $136.20   $136.20  
  Purchase #7 $139.62   12.481%   $157.046   $157.05   $157.05   $157.00  
  7 purchase totals = $1,166.29       $1,270.6509   $1,270.66   $1,270.60   $1,270.60