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 $188.95   5.282%   $198.9303   $198.93   $198.95   $198.90  
  Purchase #2 $214.89   5.485%   $226.6767   $226.68   $226.70   $226.70  
  Purchase #3 $164.33   11.183%   $182.707   $182.71   $182.70   $182.70  
  Purchase #4 $247.42   8.791%   $269.1707   $269.17   $269.15   $269.20  
  Purchase #5 $146.82   11.643%   $163.9143   $163.91   $163.90   $163.90  
  Purchase #6 $39.75   10.490%   $43.9198   $43.92   $43.90   $43.90  
  Purchase #7 $249.86   4.635%   $261.441   $261.44   $261.45   $261.40  
  7 purchase totals = $1,252.02       $1,346.7598   $1,346.76   $1,346.75   $1,346.70