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 $59.91   8.713%   $65.13   $65.13   $65.15   $65.10  
  Purchase #2 $119.41   9.452%   $130.6966   $130.70   $130.70   $130.70  
  Purchase #3 $92.53   3.874%   $96.1146   $96.11   $96.10   $96.10  
  Purchase #4 $208.44   12.579%   $234.6597   $234.66   $234.65   $234.70  
  Purchase #5 $12.67   10.406%   $13.9884   $13.99   $14.00   $14.00  
  Purchase #6 $103.28   10.530%   $114.1554   $114.16   $114.15   $114.20  
  Purchase #7 $118.38   11.449%   $131.9333   $131.93   $131.95   $131.90  
  7 purchase totals = $714.62       $786.6780   $786.68   $786.70   $786.70