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 $23.25   13.290%   $26.3399   $26.34   $26.35   $26.30  
  Purchase #2 $120.93   3.288%   $124.9062   $124.91   $124.90   $124.90  
  Purchase #3 $233.83   6.258%   $248.4631   $248.46   $248.45   $248.50  
  Purchase #4 $64.26   4.474%   $67.135   $67.14   $67.15   $67.10  
  Purchase #5 $208.52   12.449%   $234.4787   $234.48   $234.50   $234.50  
  Purchase #6 $194.94   5.175%   $205.0281   $205.03   $205.05   $205.00  
  Purchase #7 $51.99   7.106%   $55.6844   $55.68   $55.70   $55.70  
  7 purchase totals = $897.72       $962.0354   $962.04   $962.10   $962.00