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 $68.67   8.184%   $74.29   $74.29   $74.30   $74.30  
  Purchase #2 $85.55   10.303%   $94.3642   $94.36   $94.35   $94.40  
  Purchase #3 $107.70   5.853%   $114.0037   $114.00   $114.00   $114.00  
  Purchase #4 $165.57   11.547%   $184.6884   $184.69   $184.70   $184.70  
  Purchase #5 $146.79   8.338%   $159.0294   $159.03   $159.05   $159.00  
  Purchase #6 $244.50   10.328%   $269.752   $269.75   $269.75   $269.80  
  Purchase #7 $230.76   4.149%   $240.3342   $240.33   $240.35   $240.30  
  7 purchase totals = $1,049.54       $1,136.4619   $1,136.45   $1,136.50   $1,136.50