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	$233.90	7.291%	$250.9536	$250.95	$250.95	$251.00
Purchase #2	$143.52	4.823%	$150.442	$150.44	$150.45	$150.40
Purchase #3	$105.54	8.423%	$114.4296	$114.43	$114.45	$114.40
Purchase #4	$144.78	4.302%	$151.0084	$151.01	$151.00	$151.00
Purchase #5	$113.53	12.243%	$127.4295	$127.43	$127.45	$127.40
Purchase #6	$139.60	9.323%	$152.6149	$152.61	$152.60	$152.60
Purchase #7	$46.84	12.478%	$52.6847	$52.68	$52.70	$52.70
7 purchase totals =	$927.71		$999.5627	$999.55	$999.60	$999.50