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 $23.70   12.310%   $26.6175   $26.62   $26.60   $26.60  
  Purchase #2 $184.27   4.759%   $193.0394   $193.04   $193.05   $193.00  
  Purchase #3 $101.80   12.729%   $114.7581   $114.76   $114.75   $114.80  
  Purchase #4 $75.28   13.680%   $85.5783   $85.58   $85.60   $85.60  
  Purchase #5 $185.67   8.283%   $201.049   $201.05   $201.05   $201.00  
  Purchase #6 $22.38   6.384%   $23.8087   $23.81   $23.80   $23.80  
  Purchase #7 $64.52   3.738%   $66.9318   $66.93   $66.95   $66.90  
  7 purchase totals = $657.62       $711.7828   $711.79   $711.80   $711.70