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 $212.61   12.532%   $239.2543   $239.25   $239.25   $239.30  
  Purchase #2 $248.52   5.443%   $262.0469   $262.05   $262.05   $262.00  
  Purchase #3 $107.63   6.175%   $114.2762   $114.28   $114.30   $114.30  
  Purchase #4 $48.98   4.116%   $50.996   $51.00   $51.00   $51.00  
  Purchase #5 $51.93   10.122%   $57.1864   $57.19   $57.20   $57.20  
  Purchase #6 $56.29   12.743%   $63.463   $63.46   $63.45   $63.50  
  Purchase #7 $192.78   4.784%   $202.0026   $202.00   $202.00   $202.00  
  7 purchase totals = $918.74       $989.2254   $989.23   $989.25   $989.30