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 $86.90   4.233%   $90.5785   $90.58   $90.60   $90.60  
  Purchase #2 $221.43   8.356%   $239.9327   $239.93   $239.95   $239.90  
  Purchase #3 $36.68   4.347%   $38.2745   $38.27   $38.25   $38.30  
  Purchase #4 $196.80   10.299%   $217.0684   $217.07   $217.05   $217.10  
  Purchase #5 $75.99   8.213%   $82.2311   $82.23   $82.25   $82.20  
  Purchase #6 $11.68   10.275%   $12.8801   $12.88   $12.90   $12.90  
  Purchase #7 $167.60   6.173%   $177.9459   $177.95   $177.95   $177.90  
  7 purchase totals = $797.08       $858.9112   $858.91   $858.95   $858.90