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	$31.94	5.586%	$33.7242	$33.72	$33.70	$33.70
Purchase #2	$45.53	7.178%	$48.7981	$48.80	$48.80	$48.80
Purchase #3	$32.91	7.779%	$35.4701	$35.47	$35.45	$35.50
Purchase #4	$59.84	9.510%	$65.5308	$65.53	$65.55	$65.50
Purchase #5	$129.74	9.536%	$142.112	$142.11	$142.10	$142.10
Purchase #6	$51.31	12.525%	$57.7366	$57.74	$57.75	$57.70
Purchase #7	$166.30	4.522%	$173.8201	$173.82	$173.80	$173.80
7 purchase totals =	$517.57		$557.1919	$557.19	$557.15	$557.10