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	$11.70	4.870%	$12.2698	$12.27	$12.25	$12.30
Purchase #2	$75.91	9.139%	$82.8474	$82.85	$82.85	$82.80
Purchase #3	$157.74	9.336%	$172.4666	$172.47	$172.45	$172.50
Purchase #4	$156.99	8.678%	$170.6136	$170.61	$170.60	$170.60
Purchase #5	$117.71	13.504%	$133.6056	$133.61	$133.60	$133.60
Purchase #6	$229.27	8.773%	$249.3839	$249.38	$249.40	$249.40
Purchase #7	$142.78	7.245%	$153.1244	$153.12	$153.10	$153.10
7 purchase totals =	$892.10		$974.3113	$974.31	$974.25	$974.30