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	$16.54	5.340%	$17.4232	$17.42	$17.40	$17.40
Purchase #2	$141.97	12.270%	$159.3897	$159.39	$159.40	$159.40
Purchase #3	$73.54	7.543%	$79.0871	$79.09	$79.10	$79.10
Purchase #4	$35.47	11.770%	$39.6448	$39.64	$39.65	$39.60
Purchase #5	$196.78	10.352%	$217.1507	$217.15	$217.15	$217.20
Purchase #6	$78.99	13.324%	$89.5146	$89.51	$89.50	$89.50
Purchase #7	$54.96	13.868%	$62.5819	$62.58	$62.60	$62.60
7 purchase totals =	$598.25		$664.7920	$664.78	$664.80	$664.80