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	$62.83	10.213%	$69.2468	$69.25	$69.25	$69.20
Purchase #2	$122.98	3.853%	$127.7184	$127.72	$127.70	$127.70
Purchase #3	$92.87	6.781%	$99.1675	$99.17	$99.15	$99.20
Purchase #4	$99.99	8.771%	$108.7601	$108.76	$108.75	$108.80
Purchase #5	$6.72	11.495%	$7.4925	$7.49	$7.50	$7.50
Purchase #6	$49.63	6.815%	$53.0123	$53.01	$53.00	$53.00
Purchase #7	$112.54	12.240%	$126.3149	$126.31	$126.30	$126.30
7 purchase totals =	$547.56		$591.7125	$591.71	$591.65	$591.70