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	$188.76	12.353%	$212.0775	$212.08	$212.10	$212.10
Purchase #2	$114.86	12.105%	$128.7638	$128.76	$128.75	$128.80
Purchase #3	$230.69	10.397%	$254.6748	$254.67	$254.65	$254.70
Purchase #4	$53.80	5.226%	$56.6116	$56.61	$56.60	$56.60
Purchase #5	$97.36	3.417%	$100.6868	$100.69	$100.70	$100.70
Purchase #6	$174.58	13.501%	$198.15	$198.15	$198.15	$198.20
Purchase #7	$42.56	13.180%	$48.1694	$48.17	$48.15	$48.20
7 purchase totals =	$902.61		$999.1339	$999.13	$999.10	$999.30