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 $92.83   5.860%   $98.2698   $98.27   $98.25   $98.30  
  Purchase #2 $87.63   9.274%   $95.7568   $95.76   $95.75   $95.80  
  Purchase #3 $123.99   5.278%   $130.5342   $130.53   $130.55   $130.50  
  Purchase #4 $152.70   3.831%   $158.5499   $158.55   $158.55   $158.50  
  Purchase #5 $106.73   5.745%   $112.8616   $112.86   $112.85   $112.90  
  Purchase #6 $95.81   4.487%   $100.109   $100.11   $100.10   $100.10  
  Purchase #7 $197.97   8.310%   $214.4213   $214.42   $214.40   $214.40  
  7 purchase totals = $857.66       $910.5026   $910.50   $910.45   $910.50