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 $67.67   9.247%   $73.9274   $73.93   $73.95   $73.90  
  Purchase #2 $144.51   5.394%   $152.3049   $152.30   $152.30   $152.30  
  Purchase #3 $248.47   8.458%   $269.4856   $269.49   $269.50   $269.50  
  Purchase #4 $112.70   10.867%   $124.9471   $124.95   $124.95   $124.90  
  Purchase #5 $237.80   11.661%   $265.5299   $265.53   $265.55   $265.50  
  Purchase #6 $154.37   4.757%   $161.7134   $161.71   $161.70   $161.70  
  Purchase #7 $202.44   10.117%   $222.9209   $222.92   $222.90   $222.90  
  7 purchase totals = $1,167.96       $1,270.8292   $1,270.83   $1,270.85   $1,270.70