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 $65.33   12.573%   $73.5439   $73.54   $73.55   $73.50  
  Purchase #2 $29.50   9.222%   $32.2205   $32.22   $32.20   $32.20  
  Purchase #3 $129.53   4.390%   $135.2164   $135.22   $135.20   $135.20  
  Purchase #4 $250.88   4.354%   $261.8033   $261.80   $261.80   $261.80  
  Purchase #5 $202.95   4.185%   $211.4435   $211.44   $211.45   $211.40  
  Purchase #6 $197.90   5.812%   $209.4019   $209.40   $209.40   $209.40  
  Purchase #7 $78.63   8.724%   $85.4897   $85.49   $85.50   $85.50  
  7 purchase totals = $954.72       $1,009.1192   $1,009.11   $1,009.10   $1,009.00