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	$23.48	4.733%	$24.5913	$24.59	$24.60	$24.60
Purchase #2	$103.65	12.478%	$116.5834	$116.58	$116.60	$116.60
Purchase #3	$84.91	5.161%	$89.2922	$89.29	$89.30	$89.30
Purchase #4	$167.75	13.594%	$190.5539	$190.55	$190.55	$190.60
Purchase #5	$52.41	9.350%	$57.3103	$57.31	$57.30	$57.30
Purchase #6	$127.93	5.398%	$134.8357	$134.84	$134.85	$134.80
Purchase #7	$169.32	11.832%	$189.3539	$189.35	$189.35	$189.40
7 purchase totals =	$729.45		$802.5207	$802.51	$802.55	$802.60