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	$50.46	11.852%	$56.4405	$56.44	$56.45	$56.40
Purchase #2	$6.48	12.353%	$7.2805	$7.28	$7.30	$7.30
Purchase #3	$61.35	7.804%	$66.1378	$66.14	$66.15	$66.10
Purchase #4	$67.81	5.137%	$71.2934	$71.29	$71.30	$71.30
Purchase #5	$250.48	8.621%	$272.0739	$272.07	$272.05	$272.10
Purchase #6	$47.92	11.162%	$53.2688	$53.27	$53.25	$53.30
Purchase #7	$104.93	7.828%	$113.1439	$113.14	$113.15	$113.10
7 purchase totals =	$589.43		$639.6388	$639.63	$639.65	$639.60