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 $247.88   5.679%   $261.9571   $261.96   $261.95   $262.00  
  Purchase #2 $182.81   9.357%   $199.9155   $199.92   $199.90   $199.90  
  Purchase #3 $117.92   8.242%   $127.639   $127.64   $127.65   $127.60  
  Purchase #4 $250.62   3.327%   $258.9581   $258.96   $258.95   $259.00  
  Purchase #5 $75.78   11.778%   $84.7054   $84.71   $84.70   $84.70  
  Purchase #6 $167.34   6.658%   $178.4815   $178.48   $178.50   $178.50  
  Purchase #7 $207.52   11.431%   $231.2416   $231.24   $231.25   $231.20  
  7 purchase totals = $1,249.87       $1,342.8982   $1,342.91   $1,342.90   $1,342.90