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	$18.87	7.543%	$20.2934	$20.29	$20.30	$20.30
Purchase #2	$196.99	9.224%	$215.1604	$215.16	$215.15	$215.20
Purchase #3	$40.56	6.117%	$43.0411	$43.04	$43.05	$43.00
Purchase #4	$89.26	13.304%	$101.1352	$101.14	$101.15	$101.10
Purchase #5	$89.99	10.866%	$99.7683	$99.77	$99.75	$99.80
Purchase #6	$215.95	8.522%	$234.3533	$234.35	$234.35	$234.40
Purchase #7	$80.28	10.135%	$88.4164	$88.42	$88.40	$88.40
7 purchase totals =	$731.90		$802.1681	$802.17	$802.15	$802.20