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	$104.83	11.171%	$116.5406	$116.54	$116.55	$116.50
Purchase #2	$68.88	9.424%	$75.3713	$75.37	$75.35	$75.40
Purchase #3	$55.95	6.520%	$59.5979	$59.60	$59.60	$59.60
Purchase #4	$230.49	11.434%	$256.8442	$256.84	$256.85	$256.80
Purchase #5	$215.76	4.494%	$225.4563	$225.46	$225.45	$225.50
Purchase #6	$97.45	7.580%	$104.8367	$104.84	$104.85	$104.80
Purchase #7	$133.64	12.777%	$150.7152	$150.72	$150.70	$150.70
7 purchase totals =	$907.00		$989.3622	$989.37	$989.35	$989.30