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	$104.95	10.379%	$115.8428	$115.84	$115.85	$115.80
Purchase #2	$129.38	7.516%	$139.1042	$139.10	$139.10	$139.10
Purchase #3	$94.82	5.748%	$100.2703	$100.27	$100.25	$100.30
Purchase #4	$105.71	7.241%	$113.3645	$113.36	$113.35	$113.40
Purchase #5	$55.55	8.664%	$60.3629	$60.36	$60.35	$60.40
Purchase #6	$120.53	5.780%	$127.4966	$127.50	$127.50	$127.50
Purchase #7	$153.78	3.192%	$158.6887	$158.69	$158.70	$158.70
7 purchase totals =	$764.72		$815.1300	$815.12	$815.10	$815.20