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	$120.79	13.795%	$137.453	$137.45	$137.45	$137.50
Purchase #2	$30.83	6.119%	$32.7165	$32.72	$32.70	$32.70
Purchase #3	$26.77	8.253%	$28.9793	$28.98	$29.00	$29.00
Purchase #4	$172.49	5.793%	$182.4823	$182.48	$182.50	$182.50
Purchase #5	$157.86	11.685%	$176.3059	$176.31	$176.30	$176.30
Purchase #6	$118.28	8.163%	$127.9352	$127.94	$127.95	$127.90
Purchase #7	$31.48	4.637%	$32.9397	$32.94	$32.95	$32.90
7 purchase totals =	$658.50		$718.8119	$718.82	$718.85	$718.80