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 $73.50   12.509%   $82.6941   $82.69   $82.70   $82.70  
  Purchase #2 $241.67   13.215%   $273.6067   $273.61   $273.60   $273.60  
  Purchase #3 $60.60   6.256%   $64.3911   $64.39   $64.40   $64.40  
  Purchase #4 $94.39   4.646%   $98.7754   $98.78   $98.80   $98.80  
  Purchase #5 $208.76   8.344%   $226.1789   $226.18   $226.20   $226.20  
  Purchase #6 $74.40   10.773%   $82.4151   $82.42   $82.40   $82.40  
  Purchase #7 $230.39   13.579%   $261.6747   $261.67   $261.65   $261.70  
  7 purchase totals = $983.71       $1,089.7360   $1,089.74   $1,089.75   $1,089.80