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	$57.28	5.485%	$60.4218	$60.42	$60.40	$60.40
Purchase #2	$7.71	6.351%	$8.1997	$8.20	$8.20	$8.20
Purchase #3	$124.38	5.541%	$131.2719	$131.27	$131.25	$131.30
Purchase #4	$140.91	8.642%	$153.0874	$153.09	$153.10	$153.10
Purchase #5	$56.65	10.687%	$62.7042	$62.70	$62.70	$62.70
Purchase #6	$49.74	7.195%	$53.3188	$53.32	$53.30	$53.30
Purchase #7	$173.75	13.339%	$196.9265	$196.93	$196.95	$196.90
7 purchase totals =	$610.42		$665.9303	$665.93	$665.90	$665.90