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 $50.94   4.239%   $53.0993   $53.10   $53.10   $53.10  
  Purchase #2 $202.94   8.557%   $220.3056   $220.31   $220.30   $220.30  
  Purchase #3 $183.61   6.412%   $195.3831   $195.38   $195.40   $195.40  
  Purchase #4 $101.30   13.302%   $114.7749   $114.77   $114.75   $114.80  
  Purchase #5 $53.73   13.601%   $61.0378   $61.04   $61.05   $61.00  
  Purchase #6 $193.91   8.135%   $209.6846   $209.68   $209.70   $209.70  
  Purchase #7 $238.47   4.409%   $248.9841   $248.98   $249.00   $249.00  
  7 purchase totals = $1,024.90       $1,103.2694   $1,103.26   $1,103.30   $1,103.30