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 $239.50   9.264%   $261.6873   $261.69   $261.70   $261.70  
  Purchase #2 $141.50   9.349%   $154.7288   $154.73   $154.75   $154.70  
  Purchase #3 $162.52   9.142%   $177.3776   $177.38   $177.40   $177.40  
  Purchase #4 $124.30   9.643%   $136.2862   $136.29   $136.30   $136.30  
  Purchase #5 $31.48   8.492%   $34.1533   $34.15   $34.15   $34.20  
  Purchase #6 $35.64   7.676%   $38.3757   $38.38   $38.40   $38.40  
  Purchase #7 $201.45   6.126%   $213.7908   $213.79   $213.80   $213.80  
  7 purchase totals = $936.39       $1,016.3997   $1,016.41   $1,016.50   $1,016.50