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 $237.32   12.489%   $266.9589   $266.96   $266.95   $267.00  
  Purchase #2 $240.50   8.611%   $261.2095   $261.21   $261.20   $261.20  
  Purchase #3 $122.73   8.482%   $133.14   $133.14   $133.15   $133.10  
  Purchase #4 $59.73   9.224%   $65.2395   $65.24   $65.25   $65.20  
  Purchase #5 $235.32   4.187%   $245.1728   $245.17   $245.15   $245.20  
  Purchase #6 $163.87   9.646%   $179.6769   $179.68   $179.70   $179.70  
  Purchase #7 $216.79   12.573%   $244.047   $244.05   $244.05   $244.00  
  7 purchase totals = $1,276.26       $1,395.4446   $1,395.45   $1,395.45   $1,395.40