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	$204.51	12.707%	$230.4971	$230.50	$230.50	$230.50
Purchase #2	$5.52	13.814%	$6.2825	$6.28	$6.30	$6.30
Purchase #3	$44.34	6.679%	$47.3015	$47.30	$47.30	$47.30
Purchase #4	$145.54	4.103%	$151.5115	$151.51	$151.50	$151.50
Purchase #5	$127.36	9.503%	$139.463	$139.46	$139.45	$139.50
Purchase #6	$230.44	12.343%	$258.8832	$258.88	$258.90	$258.90
Purchase #7	$15.96	9.363%	$17.4543	$17.45	$17.45	$17.50
7 purchase totals =	$773.67		$851.3931	$851.38	$851.40	$851.50