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 $55.95   12.119%   $62.7306   $62.73   $62.75   $62.70  
  Purchase #2 $101.86   7.615%   $109.6166   $109.62   $109.60   $109.60  
  Purchase #3 $114.78   13.549%   $130.3315   $130.33   $130.35   $130.30  
  Purchase #4 $59.31   5.267%   $62.4339   $62.43   $62.45   $62.40  
  Purchase #5 $226.43   5.107%   $237.9938   $237.99   $238.00   $238.00  
  Purchase #6 $248.68   12.353%   $279.3994   $279.40   $279.40   $279.40  
  Purchase #7 $76.97   13.238%   $87.1593   $87.16   $87.15   $87.20  
  7 purchase totals = $883.98       $969.6651   $969.66   $969.70   $969.60