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 $65.87   5.476%   $69.477   $69.48   $69.50   $69.50  
  Purchase #2 $244.33   7.605%   $262.9113   $262.91   $262.90   $262.90  
  Purchase #3 $58.89   6.360%   $62.6354   $62.64   $62.65   $62.60  
  Purchase #4 $33.68   6.188%   $35.7641   $35.76   $35.75   $35.80  
  Purchase #5 $78.80   12.178%   $88.3963   $88.40   $88.40   $88.40  
  Purchase #6 $106.37   9.149%   $116.1018   $116.10   $116.10   $116.10  
  Purchase #7 $83.99   5.571%   $88.6691   $88.67   $88.65   $88.70  
  7 purchase totals = $671.93       $723.9550   $723.96   $723.95   $724.00