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 $244.93   6.668%   $261.2619   $261.26   $261.25   $261.30  
  Purchase #2 $46.35   6.491%   $49.3586   $49.36   $49.35   $49.40  
  Purchase #3 $173.27   4.291%   $180.705   $180.71   $180.70   $180.70  
  Purchase #4 $130.89   4.441%   $136.7028   $136.70   $136.70   $136.70  
  Purchase #5 $120.31   10.660%   $133.135   $133.14   $133.15   $133.10  
  Purchase #6 $183.99   9.741%   $201.9125   $201.91   $201.90   $201.90  
  Purchase #7 $236.92   11.413%   $263.9597   $263.96   $263.95   $264.00  
  7 purchase totals = $1,136.66       $1,227.0355   $1,227.04   $1,227.00   $1,227.10