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	$129.90	5.648%	$137.2368	$137.24	$137.25	$137.20
Purchase #2	$151.72	13.295%	$171.8912	$171.89	$171.90	$171.90
Purchase #3	$105.41	10.841%	$116.8375	$116.84	$116.85	$116.80
Purchase #4	$48.46	11.569%	$54.0663	$54.07	$54.05	$54.10
Purchase #5	$70.47	10.287%	$77.7192	$77.72	$77.70	$77.70
Purchase #6	$28.60	3.755%	$29.6739	$29.67	$29.65	$29.70
Purchase #7	$149.42	13.333%	$169.3422	$169.34	$169.35	$169.30
7 purchase totals =	$683.98		$756.7671	$756.77	$756.75	$756.70