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	$30.91	8.293%	$33.4734	$33.47	$33.45	$33.50
Purchase #2	$249.73	7.772%	$269.139	$269.14	$269.15	$269.10
Purchase #3	$159.28	8.122%	$172.2167	$172.22	$172.20	$172.20
Purchase #4	$17.70	6.140%	$18.7868	$18.79	$18.80	$18.80
Purchase #5	$134.58	8.255%	$145.6896	$145.69	$145.70	$145.70
Purchase #6	$223.52	6.601%	$238.2746	$238.27	$238.25	$238.30
Purchase #7	$127.48	12.381%	$143.2633	$143.26	$143.25	$143.30
7 purchase totals =	$943.20		$1,020.8434	$1,020.84	$1,020.80	$1,020.90