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 $61.74   13.302%   $69.9527   $69.95   $69.95   $70.00  
  Purchase #2 $56.50   12.440%   $63.5286   $63.53   $63.55   $63.50  
  Purchase #3 $49.46   7.207%   $53.0246   $53.02   $53.00   $53.00  
  Purchase #4 $143.72   10.462%   $158.756   $158.76   $158.75   $158.80  
  Purchase #5 $214.63   4.843%   $225.0245   $225.02   $225.00   $225.00  
  Purchase #6 $208.37   8.214%   $225.4855   $225.49   $225.50   $225.50  
  Purchase #7 $175.74   7.367%   $188.6868   $188.69   $188.70   $188.70  
  7 purchase totals = $910.16       $984.4587   $984.46   $984.45   $984.50