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 $249.78   4.809%   $261.7919   $261.79   $261.80   $261.80  
  Purchase #2 $73.75   5.419%   $77.7465   $77.75   $77.75   $77.70  
  Purchase #3 $161.39   9.611%   $176.9012   $176.90   $176.90   $176.90  
  Purchase #4 $186.85   13.798%   $212.6316   $212.63   $212.65   $212.60  
  Purchase #5 $248.57   13.549%   $282.2487   $282.25   $282.25   $282.20  
  Purchase #6 $206.91   10.102%   $227.812   $227.81   $227.80   $227.80  
  Purchase #7 $19.31   13.393%   $21.8962   $21.90   $21.90   $21.90  
  7 purchase totals = $1,146.56       $1,261.0281   $1,261.03   $1,261.05   $1,260.90