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	$230.43	10.792%	$255.298	$255.30	$255.30	$255.30
Purchase #2	$194.85	5.521%	$205.6077	$205.61	$205.60	$205.60
Purchase #3	$29.39	3.281%	$30.3543	$30.35	$30.35	$30.40
Purchase #4	$40.66	9.168%	$44.3877	$44.39	$44.40	$44.40
Purchase #5	$18.87	10.809%	$20.9097	$20.91	$20.90	$20.90
Purchase #6	$159.29	12.163%	$178.6644	$178.66	$178.65	$178.70
Purchase #7	$59.27	13.772%	$67.4327	$67.43	$67.45	$67.40
7 purchase totals =	$732.76		$802.6545	$802.65	$802.65	$802.70