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	$240.85	7.149%	$258.0684	$258.07	$258.05	$258.10
Purchase #2	$114.41	11.641%	$127.7285	$127.73	$127.75	$127.70
Purchase #3	$174.68	12.143%	$195.8914	$195.89	$195.90	$195.90
Purchase #4	$17.42	9.590%	$19.0906	$19.09	$19.10	$19.10
Purchase #5	$50.69	6.585%	$54.0279	$54.03	$54.05	$54.00
Purchase #6	$123.98	12.381%	$139.33	$139.33	$139.35	$139.30
Purchase #7	$172.40	9.834%	$189.3538	$189.35	$189.35	$189.40
7 purchase totals =	$894.43		$983.4906	$983.49	$983.55	$983.50