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	$55.25	9.468%	$60.4811	$60.48	$60.50	$60.50
Purchase #2	$34.44	11.124%	$38.2711	$38.27	$38.25	$38.30
Purchase #3	$87.69	13.428%	$99.465	$99.47	$99.45	$99.50
Purchase #4	$116.93	9.142%	$127.6197	$127.62	$127.60	$127.60
Purchase #5	$231.59	6.733%	$247.183	$247.18	$247.20	$247.20
Purchase #6	$191.39	7.520%	$205.7825	$205.78	$205.80	$205.80
Purchase #7	$118.62	13.550%	$134.693	$134.69	$134.70	$134.70
7 purchase totals =	$835.91		$913.4954	$913.49	$913.50	$913.60