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 $71.38   3.195%   $73.6606   $73.66   $73.65   $73.70  
  Purchase #2 $46.41   3.238%   $47.9128   $47.91   $47.90   $47.90  
  Purchase #3 $108.69   8.555%   $117.9884   $117.99   $118.00   $118.00  
  Purchase #4 $57.97   8.188%   $62.7166   $62.72   $62.70   $62.70  
  Purchase #5 $31.80   6.347%   $33.8183   $33.82   $33.80   $33.80  
  Purchase #6 $197.30   6.554%   $210.231   $210.23   $210.25   $210.20  
  Purchase #7 $159.81   11.369%   $177.9788   $177.98   $178.00   $178.00  
  7 purchase totals = $673.36       $724.3065   $724.31   $724.30   $724.30