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	$96.40	4.682%	$100.9134	$100.91	$100.90	$100.90
Purchase #2	$82.35	7.493%	$88.5205	$88.52	$88.50	$88.50
Purchase #3	$118.46	3.813%	$122.9769	$122.98	$123.00	$123.00
Purchase #4	$238.75	7.842%	$257.4728	$257.47	$257.45	$257.50
Purchase #5	$133.83	8.826%	$145.6418	$145.64	$145.65	$145.60
Purchase #6	$231.72	10.123%	$255.177	$255.18	$255.20	$255.20
Purchase #7	$21.44	11.534%	$23.9129	$23.91	$23.90	$23.90
7 purchase totals =	$922.95		$994.6153	$994.61	$994.60	$994.60