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 $57.68   6.159%   $61.2325   $61.23   $61.25   $61.20  
  Purchase #2 $206.77   5.767%   $218.6944   $218.69   $218.70   $218.70  
  Purchase #3 $20.66   13.487%   $23.4464   $23.45   $23.45   $23.40  
  Purchase #4 $238.83   11.749%   $266.8901   $266.89   $266.90   $266.90  
  Purchase #5 $15.99   12.741%   $18.0273   $18.03   $18.05   $18.00  
  Purchase #6 $22.69   10.134%   $24.9894   $24.99   $25.00   $25.00  
  Purchase #7 $67.29   6.297%   $71.5273   $71.53   $71.55   $71.50  
  7 purchase totals = $629.91       $684.8074   $684.81   $684.90   $684.70