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	$10.30	5.140%	$10.8294	$10.83	$10.85	$10.80
Purchase #2	$17.81	5.749%	$18.8339	$18.83	$18.85	$18.80
Purchase #3	$155.70	11.611%	$173.7783	$173.78	$173.80	$173.80
Purchase #4	$37.42	7.130%	$40.088	$40.09	$40.10	$40.10
Purchase #5	$56.46	10.425%	$62.346	$62.35	$62.35	$62.30
Purchase #6	$105.29	6.840%	$112.4918	$112.49	$112.50	$112.50
Purchase #7	$78.27	10.384%	$86.3976	$86.40	$86.40	$86.40
7 purchase totals =	$461.25		$504.7650	$504.77	$504.85	$504.70