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 $245.28   6.616%   $261.5077   $261.51   $261.50   $261.50  
  Purchase #2 $221.78   6.194%   $235.5171   $235.52   $235.50   $235.50  
  Purchase #3 $152.71   6.177%   $162.1429   $162.14   $162.15   $162.10  
  Purchase #4 $180.58   10.413%   $199.3838   $199.38   $199.40   $199.40  
  Purchase #5 $72.70   5.779%   $76.9013   $76.90   $76.90   $76.90  
  Purchase #6 $98.38   4.133%   $102.446   $102.45   $102.45   $102.40  
  Purchase #7 $145.96   13.683%   $165.9317   $165.93   $165.95   $165.90  
  7 purchase totals = $1,117.39       $1,203.8305   $1,203.83   $1,203.85   $1,203.70