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	$112.83	10.351%	$124.509	$124.51	$124.50	$124.50
Purchase #2	$111.63	6.257%	$118.6147	$118.61	$118.60	$118.60
Purchase #3	$75.54	6.396%	$80.3715	$80.37	$80.35	$80.40
Purchase #4	$174.30	9.188%	$190.3147	$190.31	$190.30	$190.30
Purchase #5	$122.46	4.433%	$127.8887	$127.89	$127.90	$127.90
Purchase #6	$245.55	13.687%	$279.1584	$279.16	$279.15	$279.20
Purchase #7	$15.37	7.710%	$16.555	$16.56	$16.55	$16.60
7 purchase totals =	$857.68		$937.4120	$937.41	$937.35	$937.50