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 $248.60   6.431%   $264.5875   $264.59   $264.60   $264.60  
  Purchase #2 $111.82   3.428%   $115.6532   $115.65   $115.65   $115.70  
  Purchase #3 $57.78   9.647%   $63.354   $63.35   $63.35   $63.40  
  Purchase #4 $114.93   3.859%   $119.3651   $119.37   $119.35   $119.40  
  Purchase #5 $78.49   4.291%   $81.858   $81.86   $81.85   $81.90  
  Purchase #6 $77.78   9.656%   $85.2904   $85.29   $85.30   $85.30  
  Purchase #7 $186.71   9.146%   $203.7865   $203.79   $203.80   $203.80  
  7 purchase totals = $876.11       $933.8947   $933.90   $933.90   $934.10