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	$17.73	3.516%	$18.3534	$18.35	$18.35	$18.40
Purchase #2	$214.68	4.144%	$223.5763	$223.58	$223.60	$223.60
Purchase #3	$193.28	7.521%	$207.8166	$207.82	$207.80	$207.80
Purchase #4	$93.65	5.145%	$98.4683	$98.47	$98.45	$98.50
Purchase #5	$19.83	3.756%	$20.5748	$20.57	$20.55	$20.60
Purchase #6	$97.26	8.747%	$105.7673	$105.77	$105.75	$105.80
Purchase #7	$85.49	4.578%	$89.4037	$89.40	$89.40	$89.40
7 purchase totals =	$721.92		$763.9604	$763.96	$763.90	$764.10