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	$15.71	5.689%	$16.6037	$16.60	$16.60	$16.60
Purchase #2	$49.84	7.551%	$53.6034	$53.60	$53.60	$53.60
Purchase #3	$17.36	13.212%	$19.6536	$19.65	$19.65	$19.70
Purchase #4	$96.71	12.759%	$109.0492	$109.05	$109.05	$109.00
Purchase #5	$44.95	9.614%	$49.2715	$49.27	$49.25	$49.30
Purchase #6	$106.76	4.211%	$111.2557	$111.26	$111.25	$111.30
Purchase #7	$124.48	11.769%	$139.1301	$139.13	$139.15	$139.10
7 purchase totals =	$455.81		$498.5672	$498.56	$498.55	$498.60