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 $64.37   4.473%   $67.2493   $67.25   $67.25   $67.20  
  Purchase #2 $158.68   3.834%   $164.7638   $164.76   $164.75   $164.80  
  Purchase #3 $36.57   11.735%   $40.8615   $40.86   $40.85   $40.90  
  Purchase #4 $76.25   11.325%   $84.8853   $84.89   $84.90   $84.90  
  Purchase #5 $57.66   8.130%   $62.3478   $62.35   $62.35   $62.30  
  Purchase #6 $163.65   4.584%   $171.1517   $171.15   $171.15   $171.20  
  Purchase #7 $245.81   12.476%   $276.4773   $276.48   $276.50   $276.50  
  7 purchase totals = $802.99       $867.7367   $867.74   $867.75   $867.80