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	$247.96	4.384%	$258.8306	$258.83	$258.85	$258.80
Purchase #2	$39.58	5.160%	$41.6223	$41.62	$41.60	$41.60
Purchase #3	$111.96	13.858%	$127.4754	$127.48	$127.50	$127.50
Purchase #4	$20.90	10.862%	$23.1702	$23.17	$23.15	$23.20
Purchase #5	$60.77	7.349%	$65.236	$65.24	$65.25	$65.20
Purchase #6	$17.93	3.271%	$18.5165	$18.52	$18.50	$18.50
Purchase #7	$77.68	6.374%	$82.6313	$82.63	$82.65	$82.60
7 purchase totals =	$576.78		$617.4823	$617.49	$617.50	$617.40