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	$66.47	11.160%	$73.8881	$73.89	$73.90	$73.90
Purchase #2	$106.66	5.124%	$112.1253	$112.13	$112.15	$112.10
Purchase #3	$122.35	12.564%	$137.7221	$137.72	$137.70	$137.70
Purchase #4	$201.84	13.681%	$229.4537	$229.45	$229.45	$229.50
Purchase #5	$68.25	13.470%	$77.4433	$77.44	$77.45	$77.40
Purchase #6	$100.87	4.604%	$105.5141	$105.51	$105.50	$105.50
Purchase #7	$114.51	8.558%	$124.3098	$124.31	$124.30	$124.30
7 purchase totals =	$780.95		$860.4564	$860.45	$860.45	$860.40