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	$13.92	11.783%	$15.5602	$15.56	$15.55	$15.60
Purchase #2	$235.47	7.522%	$253.1821	$253.18	$253.20	$253.20
Purchase #3	$83.40	6.477%	$88.8018	$88.80	$88.80	$88.80
Purchase #4	$118.60	7.459%	$127.4464	$127.45	$127.45	$127.40
Purchase #5	$20.75	6.267%	$22.0504	$22.05	$22.05	$22.10
Purchase #6	$36.66	4.511%	$38.3137	$38.31	$38.30	$38.30
Purchase #7	$224.95	13.558%	$255.4487	$255.45	$255.45	$255.40
7 purchase totals =	$733.75		$800.8033	$800.80	$800.80	$800.80