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	$56.86	3.546%	$58.8763	$58.88	$58.90	$58.90
Purchase #2	$24.64	11.273%	$27.4177	$27.42	$27.40	$27.40
Purchase #3	$197.70	4.126%	$205.8571	$205.86	$205.85	$205.90
Purchase #4	$236.64	9.259%	$258.5505	$258.55	$258.55	$258.60
Purchase #5	$194.28	5.762%	$205.4744	$205.47	$205.45	$205.50
Purchase #6	$113.68	12.271%	$127.6297	$127.63	$127.65	$127.60
Purchase #7	$179.66	6.240%	$190.8708	$190.87	$190.85	$190.90
7 purchase totals =	$1,003.46		$1,074.6765	$1,074.68	$1,074.65	$1,074.80