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	$19.54	4.784%	$20.4748	$20.47	$20.45	$20.50
Purchase #2	$101.91	12.491%	$114.6396	$114.64	$114.65	$114.60
Purchase #3	$75.73	13.409%	$85.8846	$85.88	$85.90	$85.90
Purchase #4	$107.53	3.836%	$111.6549	$111.65	$111.65	$111.70
Purchase #5	$229.80	6.382%	$244.4658	$244.47	$244.45	$244.50
Purchase #6	$205.85	8.729%	$223.8186	$223.82	$223.80	$223.80
Purchase #7	$115.37	12.277%	$129.534	$129.53	$129.55	$129.50
7 purchase totals =	$855.73		$930.4723	$930.46	$930.45	$930.50