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	$15.99	9.178%	$17.4576	$17.46	$17.45	$17.50
Purchase #2	$89.56	11.151%	$99.5468	$99.55	$99.55	$99.50
Purchase #3	$114.27	5.255%	$120.2749	$120.27	$120.25	$120.30
Purchase #4	$89.85	12.838%	$101.3849	$101.38	$101.40	$101.40
Purchase #5	$197.77	8.322%	$214.2284	$214.23	$214.25	$214.20
Purchase #6	$138.82	12.865%	$156.6792	$156.68	$156.70	$156.70
Purchase #7	$116.31	9.645%	$127.5281	$127.53	$127.55	$127.50
7 purchase totals =	$762.57		$837.0999	$837.10	$837.15	$837.10