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	$73.73	10.559%	$81.5152	$81.52	$81.50	$81.50
Purchase #2	$11.51	12.191%	$12.9132	$12.91	$12.90	$12.90
Purchase #3	$155.56	11.748%	$173.8352	$173.84	$173.85	$173.80
Purchase #4	$199.68	9.398%	$218.4459	$218.45	$218.45	$218.40
Purchase #5	$212.83	9.751%	$233.5831	$233.58	$233.60	$233.60
Purchase #6	$114.37	7.464%	$122.9066	$122.91	$122.90	$122.90
Purchase #7	$37.73	11.692%	$42.1414	$42.14	$42.15	$42.10
7 purchase totals =	$805.41		$885.3406	$885.35	$885.35	$885.20