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 $69.62   6.209%   $73.9427   $73.94   $73.95   $73.90  
  Purchase #2 $248.67   12.196%   $278.9978   $279.00   $279.00   $279.00  
  Purchase #3 $208.76   8.873%   $227.2833   $227.28   $227.30   $227.30  
  Purchase #4 $148.89   13.589%   $169.1227   $169.12   $169.10   $169.10  
  Purchase #5 $65.59   12.813%   $73.994   $73.99   $74.00   $74.00  
  Purchase #6 $100.63   7.246%   $107.9216   $107.92   $107.90   $107.90  
  Purchase #7 $14.67   13.745%   $16.6864   $16.69   $16.70   $16.70  
  7 purchase totals = $856.83       $947.9485   $947.94   $947.95   $947.90