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	$47.99	13.729%	$54.5785	$54.58	$54.60	$54.60
Purchase #2	$35.56	13.656%	$40.4161	$40.42	$40.40	$40.40
Purchase #3	$111.75	5.445%	$117.8348	$117.83	$117.85	$117.80
Purchase #4	$83.99	5.219%	$88.3734	$88.37	$88.35	$88.40
Purchase #5	$193.51	7.215%	$207.4717	$207.47	$207.45	$207.50
Purchase #6	$27.91	3.665%	$28.9329	$28.93	$28.95	$28.90
Purchase #7	$90.31	10.485%	$99.779	$99.78	$99.80	$99.80
7 purchase totals =	$591.02		$637.3864	$637.38	$637.40	$637.40