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	$203.60	9.222%	$222.376	$222.38	$222.40	$222.40
Purchase #2	$171.77	9.819%	$188.6361	$188.64	$188.65	$188.60
Purchase #3	$198.33	9.798%	$217.7624	$217.76	$217.75	$217.80
Purchase #4	$142.68	5.497%	$150.5231	$150.52	$150.50	$150.50
Purchase #5	$11.78	8.127%	$12.7374	$12.74	$12.75	$12.70
Purchase #6	$65.72	11.341%	$73.1733	$73.17	$73.15	$73.20
Purchase #7	$32.47	3.619%	$33.6451	$33.65	$33.65	$33.60
7 purchase totals =	$826.35		$898.8534	$898.86	$898.85	$898.80