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	$124.27	7.343%	$133.3951	$133.40	$133.40	$133.40
Purchase #2	$74.82	3.610%	$77.521	$77.52	$77.50	$77.50
Purchase #3	$50.62	13.838%	$57.6248	$57.62	$57.60	$57.60
Purchase #4	$65.25	9.821%	$71.6582	$71.66	$71.65	$71.70
Purchase #5	$99.87	6.557%	$106.4185	$106.42	$106.40	$106.40
Purchase #6	$99.61	4.346%	$103.9391	$103.94	$103.95	$103.90
Purchase #7	$18.82	12.268%	$21.1288	$21.13	$21.15	$21.10
7 purchase totals =	$533.26		$571.6855	$571.69	$571.65	$571.60