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	$113.76	12.170%	$127.6046	$127.60	$127.60	$127.60
Purchase #2	$53.77	6.191%	$57.0989	$57.10	$57.10	$57.10
Purchase #3	$214.80	8.828%	$233.7625	$233.76	$233.75	$233.80
Purchase #4	$55.91	9.854%	$61.4194	$61.42	$61.40	$61.40
Purchase #5	$51.88	13.823%	$59.0514	$59.05	$59.05	$59.10
Purchase #6	$77.92	8.385%	$84.4536	$84.45	$84.45	$84.50
Purchase #7	$19.27	6.189%	$20.4626	$20.46	$20.45	$20.50
7 purchase totals =	$587.31		$643.8530	$643.84	$643.80	$644.00