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 $36.53   4.701%   $38.2473   $38.25   $38.25   $38.20  
  Purchase #2 $248.41   12.237%   $278.8079   $278.81   $278.80   $278.80  
  Purchase #3 $65.69   8.428%   $71.2264   $71.23   $71.25   $71.20  
  Purchase #4 $182.66   4.325%   $190.56   $190.56   $190.55   $190.60  
  Purchase #5 $76.51   10.304%   $84.3936   $84.39   $84.40   $84.40  
  Purchase #6 $133.39   13.339%   $151.1829   $151.18   $151.20   $151.20  
  Purchase #7 $134.74   13.209%   $152.5378   $152.54   $152.55   $152.50  
  7 purchase totals = $877.93       $966.9559   $966.96   $967.00   $966.90