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	$16.83	11.587%	$18.7801	$18.78	$18.80	$18.80
Purchase #2	$13.61	3.698%	$14.1133	$14.11	$14.10	$14.10
Purchase #3	$223.85	10.459%	$247.2625	$247.26	$247.25	$247.30
Purchase #4	$223.72	9.868%	$245.7967	$245.80	$245.80	$245.80
Purchase #5	$170.53	8.540%	$185.0933	$185.09	$185.10	$185.10
Purchase #6	$106.40	9.568%	$116.5804	$116.58	$116.60	$116.60
Purchase #7	$170.73	11.730%	$190.7566	$190.76	$190.75	$190.80
7 purchase totals =	$925.67		$1,018.3829	$1,018.38	$1,018.40	$1,018.50