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 $54.35   9.554%   $59.5426   $59.54   $59.55   $59.50  
  Purchase #2 $196.61   4.348%   $205.1586   $205.16   $205.15   $205.20  
  Purchase #3 $141.57   3.307%   $146.2517   $146.25   $146.25   $146.30  
  Purchase #4 $105.99   9.615%   $116.1809   $116.18   $116.20   $116.20  
  Purchase #5 $32.68   6.848%   $34.9179   $34.92   $34.90   $34.90  
  Purchase #6 $69.31   7.719%   $74.66   $74.66   $74.65   $74.70  
  Purchase #7 $35.63   4.379%   $37.1902   $37.19   $37.20   $37.20  
  7 purchase totals = $636.14       $673.9019   $673.90   $673.90   $674.00