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 $54.76   11.249%   $60.92   $60.92   $60.90   $60.90  
  Purchase #2 $231.64   6.124%   $245.8256   $245.83   $245.85   $245.80  
  Purchase #3 $189.41   3.163%   $195.401   $195.40   $195.40   $195.40  
  Purchase #4 $76.87   3.105%   $79.2568   $79.26   $79.25   $79.30  
  Purchase #5 $233.66   11.847%   $261.3417   $261.34   $261.35   $261.30  
  Purchase #6 $228.89   5.409%   $241.2707   $241.27   $241.25   $241.30  
  Purchase #7 $131.78   12.183%   $147.8348   $147.83   $147.85   $147.80  
  7 purchase totals = $1,147.01       $1,231.8506   $1,231.85   $1,231.85   $1,231.80