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	$237.47	5.352%	$250.1794	$250.18	$250.20	$250.20
Purchase #2	$52.82	12.319%	$59.3269	$59.33	$59.35	$59.30
Purchase #3	$53.26	13.628%	$60.5183	$60.52	$60.50	$60.50
Purchase #4	$158.39	10.716%	$175.3631	$175.36	$175.35	$175.40
Purchase #5	$57.92	12.352%	$65.0743	$65.07	$65.05	$65.10
Purchase #6	$15.79	11.721%	$17.6407	$17.64	$17.65	$17.60
Purchase #7	$118.66	7.159%	$127.1549	$127.15	$127.15	$127.20
7 purchase totals =	$694.31		$755.2576	$755.25	$755.25	$755.30