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	$212.51	8.856%	$231.3299	$231.33	$231.35	$231.30
Purchase #2	$16.81	11.848%	$18.8016	$18.80	$18.80	$18.80
Purchase #3	$129.50	7.831%	$139.6411	$139.64	$139.65	$139.60
Purchase #4	$142.92	10.811%	$158.3711	$158.37	$158.35	$158.40
Purchase #5	$56.82	5.151%	$59.7468	$59.75	$59.75	$59.70
Purchase #6	$151.98	9.648%	$166.643	$166.64	$166.65	$166.60
Purchase #7	$207.88	3.792%	$215.7628	$215.76	$215.75	$215.80
7 purchase totals =	$918.42		$990.2963	$990.29	$990.30	$990.20