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 $229.91   13.510%   $260.9708   $260.97   $260.95   $261.00  
  Purchase #2 $138.33   3.377%   $143.0014   $143.00   $143.00   $143.00  
  Purchase #3 $195.42   13.803%   $222.3938   $222.39   $222.40   $222.40  
  Purchase #4 $84.71   12.223%   $95.0641   $95.06   $95.05   $95.10  
  Purchase #5 $109.43   4.371%   $114.2132   $114.21   $114.20   $114.20  
  Purchase #6 $162.85   9.677%   $178.609   $178.61   $178.60   $178.60  
  Purchase #7 $238.51   6.178%   $253.2451   $253.25   $253.25   $253.20  
  7 purchase totals = $1,159.16       $1,267.4974   $1,267.49   $1,267.45   $1,267.50