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	$19.97	8.474%	$21.6623	$21.66	$21.65	$21.70
Purchase #2	$154.41	12.510%	$173.7267	$173.73	$173.75	$173.70
Purchase #3	$55.80	4.145%	$58.1129	$58.11	$58.10	$58.10
Purchase #4	$52.42	13.538%	$59.5166	$59.52	$59.50	$59.50
Purchase #5	$38.47	3.153%	$39.683	$39.68	$39.70	$39.70
Purchase #6	$68.73	5.167%	$72.2813	$72.28	$72.30	$72.30
Purchase #7	$90.58	6.447%	$96.4197	$96.42	$96.40	$96.40
7 purchase totals =	$480.38		$521.4025	$521.40	$521.40	$521.40