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 $63.62   8.813%   $69.2268   $69.23   $69.25   $69.20  
  Purchase #2 $190.54   12.692%   $214.7233   $214.72   $214.70   $214.70  
  Purchase #3 $136.26   8.757%   $148.1923   $148.19   $148.20   $148.20  
  Purchase #4 $41.98   4.705%   $43.9552   $43.96   $43.95   $44.00  
  Purchase #5 $232.64   12.347%   $261.3641   $261.36   $261.35   $261.40  
  Purchase #6 $247.73   5.613%   $261.6351   $261.64   $261.65   $261.60  
  Purchase #7 $248.33   10.419%   $274.2035   $274.20   $274.20   $274.20  
  7 purchase totals = $1,161.10       $1,273.3003   $1,273.30   $1,273.30   $1,273.30