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	$166.85	11.414%	$185.8943	$185.89	$185.90	$185.90
Purchase #2	$156.64	7.851%	$168.9378	$168.94	$168.95	$168.90
Purchase #3	$158.87	10.603%	$175.715	$175.72	$175.70	$175.70
Purchase #4	$77.49	3.139%	$79.9224	$79.92	$79.90	$79.90
Purchase #5	$49.45	5.479%	$52.1594	$52.16	$52.15	$52.20
Purchase #6	$114.73	7.703%	$123.5677	$123.57	$123.55	$123.60
Purchase #7	$166.26	9.509%	$182.0697	$182.07	$182.05	$182.10
7 purchase totals =	$890.29		$968.2663	$968.27	$968.20	$968.30