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	$143.35	7.204%	$153.6769	$153.68	$153.70	$153.70
Purchase #2	$173.48	13.518%	$196.931	$196.93	$196.95	$196.90
Purchase #3	$114.77	3.370%	$118.6377	$118.64	$118.65	$118.60
Purchase #4	$59.59	9.294%	$65.1283	$65.13	$65.15	$65.10
Purchase #5	$123.91	12.549%	$139.4595	$139.46	$139.45	$139.50
Purchase #6	$241.70	7.184%	$259.0637	$259.06	$259.05	$259.10
Purchase #7	$143.68	3.539%	$148.7648	$148.76	$148.75	$148.80
7 purchase totals =	$1,000.48		$1,081.6619	$1,081.66	$1,081.70	$1,081.70