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	$56.87	5.281%	$59.8733	$59.87	$59.85	$59.90
Purchase #2	$61.66	4.234%	$64.2707	$64.27	$64.25	$64.30
Purchase #3	$173.28	13.841%	$197.2637	$197.26	$197.25	$197.30
Purchase #4	$146.39	7.132%	$156.8305	$156.83	$156.85	$156.80
Purchase #5	$53.92	12.451%	$60.6336	$60.63	$60.65	$60.60
Purchase #6	$55.92	9.360%	$61.1541	$61.15	$61.15	$61.20
Purchase #7	$140.60	10.435%	$155.2716	$155.27	$155.25	$155.30
7 purchase totals =	$688.64		$755.2975	$755.28	$755.25	$755.40