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 $211.74   10.529%   $234.0341   $234.03   $234.05   $234.00  
  Purchase #2 $103.34   10.712%   $114.4098   $114.41   $114.40   $114.40  
  Purchase #3 $8.25   8.250%   $8.9306   $8.93   $8.95   $8.90  
  Purchase #4 $44.51   4.732%   $46.6162   $46.62   $46.60   $46.60  
  Purchase #5 $247.46   5.771%   $261.7409   $261.74   $261.75   $261.70  
  Purchase #6 $97.29   4.434%   $101.6038   $101.60   $101.60   $101.60  
  Purchase #7 $23.72   9.666%   $26.0128   $26.01   $26.00   $26.00  
  7 purchase totals = $736.31       $793.3482   $793.34   $793.35   $793.20