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	$136.52	6.687%	$145.6491	$145.65	$145.65	$145.60
Purchase #2	$133.86	11.187%	$148.8349	$148.83	$148.85	$148.80
Purchase #3	$156.37	7.771%	$168.5215	$168.52	$168.50	$168.50
Purchase #4	$59.38	5.726%	$62.7801	$62.78	$62.80	$62.80
Purchase #5	$246.66	10.162%	$271.7256	$271.73	$271.75	$271.70
Purchase #6	$18.82	7.147%	$20.1651	$20.17	$20.15	$20.20
Purchase #7	$178.73	9.679%	$196.0293	$196.03	$196.05	$196.00
7 purchase totals =	$930.34		$1,013.7056	$1,013.71	$1,013.75	$1,013.60