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	$25.77	13.649%	$29.2873	$29.29	$29.30	$29.30
Purchase #2	$222.58	13.793%	$253.2805	$253.28	$253.30	$253.30
Purchase #3	$111.93	13.650%	$127.2084	$127.21	$127.20	$127.20
Purchase #4	$235.75	7.341%	$253.0564	$253.06	$253.05	$253.10
Purchase #5	$136.43	3.562%	$141.2896	$141.29	$141.30	$141.30
Purchase #6	$154.37	4.733%	$161.6763	$161.68	$161.70	$161.70
Purchase #7	$188.66	4.237%	$196.6535	$196.65	$196.65	$196.70
7 purchase totals =	$1,075.49		$1,162.4520	$1,162.46	$1,162.50	$1,162.60