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	$5.46	4.804%	$5.7223	$5.72	$5.70	$5.70
Purchase #2	$228.72	11.852%	$255.8279	$255.83	$255.85	$255.80
Purchase #3	$12.39	4.249%	$12.9165	$12.92	$12.90	$12.90
Purchase #4	$132.68	13.294%	$150.3185	$150.32	$150.30	$150.30
Purchase #5	$148.72	6.243%	$158.0046	$158.00	$158.00	$158.00
Purchase #6	$84.40	10.294%	$93.0881	$93.09	$93.10	$93.10
Purchase #7	$82.95	7.858%	$89.4682	$89.47	$89.45	$89.50
7 purchase totals =	$695.32		$765.3461	$765.35	$765.30	$765.30