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	$19.73	5.509%	$20.8169	$20.82	$20.80	$20.80
Purchase #2	$243.59	11.598%	$271.8416	$271.84	$271.85	$271.80
Purchase #3	$54.38	12.480%	$61.1666	$61.17	$61.15	$61.20
Purchase #4	$158.80	5.613%	$167.7134	$167.71	$167.70	$167.70
Purchase #5	$116.45	5.408%	$122.7476	$122.75	$122.75	$122.70
Purchase #6	$72.60	8.561%	$78.8153	$78.82	$78.80	$78.80
Purchase #7	$101.61	4.486%	$106.1682	$106.17	$106.15	$106.20
7 purchase totals =	$767.16		$829.2696	$829.28	$829.20	$829.20