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	$11.90	10.666%	$13.1693	$13.17	$13.15	$13.20
Purchase #2	$141.29	4.536%	$147.6989	$147.70	$147.70	$147.70
Purchase #3	$118.72	7.276%	$127.3581	$127.36	$127.35	$127.40
Purchase #4	$106.55	7.549%	$114.5935	$114.59	$114.60	$114.60
Purchase #5	$146.31	9.504%	$160.2153	$160.22	$160.20	$160.20
Purchase #6	$145.64	3.480%	$150.7083	$150.71	$150.70	$150.70
Purchase #7	$119.99	6.113%	$127.325	$127.33	$127.35	$127.30
7 purchase totals =	$790.40		$841.0684	$841.08	$841.05	$841.10