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	$14.96	3.227%	$15.4428	$15.44	$15.45	$15.40
Purchase #2	$41.96	6.546%	$44.7067	$44.71	$44.70	$44.70
Purchase #3	$135.68	13.339%	$153.7784	$153.78	$153.80	$153.80
Purchase #4	$243.64	13.252%	$275.9272	$275.93	$275.95	$275.90
Purchase #5	$164.27	5.542%	$173.3738	$173.37	$173.35	$173.40
Purchase #6	$51.94	13.635%	$59.022	$59.02	$59.00	$59.00
Purchase #7	$122.51	12.568%	$137.9071	$137.91	$137.90	$137.90
7 purchase totals =	$774.96		$860.1580	$860.16	$860.15	$860.10