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 $76.63   11.779%   $85.6562   $85.66   $85.65   $85.70  
  Purchase #2 $212.61   4.549%   $222.2816   $222.28   $222.30   $222.30  
  Purchase #3 $198.90   10.448%   $219.6811   $219.68   $219.70   $219.70  
  Purchase #4 $49.38   9.230%   $53.9378   $53.94   $53.95   $53.90  
  Purchase #5 $175.50   5.548%   $185.2367   $185.24   $185.25   $185.20  
  Purchase #6 $240.61   8.387%   $260.79   $260.79   $260.80   $260.80  
  Purchase #7 $104.81   8.834%   $114.0689   $114.07   $114.05   $114.10  
  7 purchase totals = $1,058.44       $1,141.6523   $1,141.66   $1,141.70   $1,141.70