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 $29.67   8.723%   $32.2581   $32.26   $32.25   $32.30  
  Purchase #2 $129.93   3.688%   $134.7218   $134.72   $134.70   $134.70  
  Purchase #3 $178.86   8.387%   $193.861   $193.86   $193.85   $193.90  
  Purchase #4 $24.91   10.333%   $27.484   $27.48   $27.50   $27.50  
  Purchase #5 $149.88   8.834%   $163.1204   $163.12   $163.10   $163.10  
  Purchase #6 $106.45   6.857%   $113.7493   $113.75   $113.75   $113.70  
  Purchase #7 $50.76   9.357%   $55.5096   $55.51   $55.50   $55.50  
  7 purchase totals = $670.46       $720.7042   $720.70   $720.65   $720.70