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 $24.80   5.759%   $26.2282   $26.23   $26.25   $26.20  
  Purchase #2 $152.57   5.444%   $160.8759   $160.88   $160.90   $160.90  
  Purchase #3 $123.66   11.600%   $138.0046   $138.00   $138.00   $138.00  
  Purchase #4 $76.83   8.823%   $83.6087   $83.61   $83.60   $83.60  
  Purchase #5 $250.76   6.388%   $266.7785   $266.78   $266.80   $266.80  
  Purchase #6 $51.86   5.145%   $54.5282   $54.53   $54.55   $54.50  
  Purchase #7 $216.61   10.318%   $238.9598   $238.96   $238.95   $239.00  
  7 purchase totals = $897.09       $968.9839   $968.99   $969.05   $969.00