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	$9.89	10.178%	$10.8966	$10.90	$10.90	$10.90
Purchase #2	$217.67	12.643%	$245.19	$245.19	$245.20	$245.20
Purchase #3	$74.26	5.282%	$78.1824	$78.18	$78.20	$78.20
Purchase #4	$146.72	13.224%	$166.1223	$166.12	$166.10	$166.10
Purchase #5	$176.73	6.639%	$188.4631	$188.46	$188.45	$188.50
Purchase #6	$138.39	9.622%	$151.7059	$151.71	$151.70	$151.70
Purchase #7	$207.42	8.623%	$225.3058	$225.31	$225.30	$225.30
7 purchase totals =	$971.08		$1,065.8661	$1,065.87	$1,065.85	$1,065.90