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	$24.63	12.235%	$27.6435	$27.64	$27.65	$27.60
Purchase #2	$219.55	11.560%	$244.93	$244.93	$244.95	$244.90
Purchase #3	$64.67	13.857%	$73.6313	$73.63	$73.65	$73.60
Purchase #4	$128.49	11.662%	$143.4745	$143.47	$143.45	$143.50
Purchase #5	$122.38	4.123%	$127.4257	$127.43	$127.45	$127.40
Purchase #6	$73.54	5.415%	$77.5222	$77.52	$77.50	$77.50
Purchase #7	$160.31	7.299%	$172.011	$172.01	$172.00	$172.00
7 purchase totals =	$793.57		$866.6382	$866.63	$866.65	$866.50