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 $199.80   10.244%   $220.2675   $220.27   $220.25   $220.30  
  Purchase #2 $113.99   8.233%   $123.3748   $123.37   $123.35   $123.40  
  Purchase #3 $180.90   10.255%   $199.4513   $199.45   $199.45   $199.50  
  Purchase #4 $100.49   10.658%   $111.2002   $111.20   $111.20   $111.20  
  Purchase #5 $237.85   4.446%   $248.4248   $248.42   $248.40   $248.40  
  Purchase #6 $46.27   12.430%   $52.0214   $52.02   $52.00   $52.00  
  Purchase #7 $248.92   5.247%   $261.9808   $261.98   $262.00   $262.00  
  7 purchase totals = $1,128.22       $1,216.7208   $1,216.71   $1,216.65   $1,216.80