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	$16.47	13.406%	$18.678	$18.68	$18.70	$18.70
Purchase #2	$242.52	4.619%	$253.722	$253.72	$253.70	$253.70
Purchase #3	$162.77	11.255%	$181.0898	$181.09	$181.10	$181.10
Purchase #4	$135.60	9.698%	$148.7505	$148.75	$148.75	$148.80
Purchase #5	$155.32	12.596%	$174.8841	$174.88	$174.90	$174.90
Purchase #6	$85.83	4.760%	$89.9155	$89.92	$89.90	$89.90
Purchase #7	$131.77	13.725%	$149.8554	$149.86	$149.85	$149.90
7 purchase totals =	$930.28		$1,016.8953	$1,016.90	$1,016.90	$1,017.00