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	$249.31	3.810%	$258.8087	$258.81	$258.80	$258.80
Purchase #2	$26.76	12.555%	$30.1197	$30.12	$30.10	$30.10
Purchase #3	$243.27	13.152%	$275.2649	$275.26	$275.25	$275.30
Purchase #4	$45.78	5.388%	$48.2466	$48.25	$48.25	$48.20
Purchase #5	$112.29	13.711%	$127.6861	$127.69	$127.70	$127.70
Purchase #6	$130.29	9.206%	$142.2845	$142.28	$142.30	$142.30
Purchase #7	$73.47	5.222%	$77.3066	$77.31	$77.30	$77.30
7 purchase totals =	$881.17		$959.7171	$959.72	$959.70	$959.70