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	$138.49	11.601%	$154.5562	$154.56	$154.55	$154.60
Purchase #2	$95.68	5.265%	$100.7176	$100.72	$100.70	$100.70
Purchase #3	$231.65	13.584%	$263.1173	$263.12	$263.10	$263.10
Purchase #4	$62.95	3.551%	$65.1854	$65.19	$65.20	$65.20
Purchase #5	$237.30	7.760%	$255.7145	$255.71	$255.70	$255.70
Purchase #6	$122.54	11.109%	$136.153	$136.15	$136.15	$136.20
Purchase #7	$24.47	11.568%	$27.3007	$27.30	$27.30	$27.30
7 purchase totals =	$913.08		$1,002.7447	$1,002.75	$1,002.70	$1,002.80