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	$62.58	11.259%	$69.6259	$69.63	$69.65	$69.60
Purchase #2	$32.77	3.837%	$34.0274	$34.03	$34.05	$34.00
Purchase #3	$139.37	7.643%	$150.022	$150.02	$150.00	$150.00
Purchase #4	$124.82	11.466%	$139.1319	$139.13	$139.15	$139.10
Purchase #5	$72.27	8.352%	$78.306	$78.31	$78.30	$78.30
Purchase #6	$76.91	4.572%	$80.4263	$80.43	$80.45	$80.40
Purchase #7	$29.87	8.346%	$32.363	$32.36	$32.35	$32.40
7 purchase totals =	$538.59		$583.9025	$583.91	$583.95	$583.80