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 $26.44   13.565%   $30.0266   $30.03   $30.05   $30.00  
  Purchase #2 $249.84   4.537%   $261.1752   $261.18   $261.20   $261.20  
  Purchase #3 $91.35   11.397%   $101.7612   $101.76   $101.75   $101.80  
  Purchase #4 $66.46   5.106%   $69.8534   $69.85   $69.85   $69.90  
  Purchase #5 $229.26   11.530%   $255.6937   $255.69   $255.70   $255.70  
  Purchase #6 $122.51   6.121%   $130.0088   $130.01   $130.00   $130.00  
  Purchase #7 $142.83   6.828%   $152.5824   $152.58   $152.60   $152.60  
  7 purchase totals = $928.69       $1,001.1013   $1,001.10   $1,001.15   $1,001.20