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 $59.75   11.810%   $66.8065   $66.81   $66.80   $66.80  
  Purchase #2 $163.57   7.812%   $176.3481   $176.35   $176.35   $176.30  
  Purchase #3 $189.74   5.808%   $200.7601   $200.76   $200.75   $200.80  
  Purchase #4 $218.99   12.207%   $245.7221   $245.72   $245.70   $245.70  
  Purchase #5 $49.50   7.581%   $53.2526   $53.25   $53.25   $53.30  
  Purchase #6 $185.34   4.665%   $193.9861   $193.99   $194.00   $194.00  
  Purchase #7 $27.70   10.556%   $30.624   $30.62   $30.60   $30.60  
  7 purchase totals = $894.59       $967.4995   $967.50   $967.45   $967.50