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	$122.28	13.814%	$139.1718	$139.17	$139.15	$139.20
Purchase #2	$193.57	10.677%	$214.2375	$214.24	$214.25	$214.20
Purchase #3	$32.72	9.702%	$35.8945	$35.89	$35.90	$35.90
Purchase #4	$120.95	5.151%	$127.1801	$127.18	$127.20	$127.20
Purchase #5	$82.70	8.545%	$89.7667	$89.77	$89.75	$89.80
Purchase #6	$155.49	3.624%	$161.125	$161.13	$161.15	$161.10
Purchase #7	$33.56	13.465%	$38.0789	$38.08	$38.10	$38.10
7 purchase totals =	$741.27		$805.4545	$805.46	$805.50	$805.50