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 $24.55   6.569%   $26.1627   $26.16   $26.15   $26.20  
  Purchase #2 $200.71   12.342%   $225.4816   $225.48   $225.50   $225.50  
  Purchase #3 $238.39   4.168%   $248.3261   $248.33   $248.35   $248.30  
  Purchase #4 $141.92   3.252%   $146.5352   $146.54   $146.55   $146.50  
  Purchase #5 $21.76   5.364%   $22.9272   $22.93   $22.95   $22.90  
  Purchase #6 $102.33   3.550%   $105.9627   $105.96   $105.95   $106.00  
  Purchase #7 $81.99   11.721%   $91.6   $91.60   $91.60   $91.60  
  7 purchase totals = $811.65       $866.9955   $867.00   $867.05   $867.00