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	$229.56	5.646%	$242.521	$242.52	$242.50	$242.50
Purchase #2	$162.78	9.407%	$178.0927	$178.09	$178.10	$178.10
Purchase #3	$64.51	8.680%	$70.1095	$70.11	$70.10	$70.10
Purchase #4	$125.80	3.571%	$130.2923	$130.29	$130.30	$130.30
Purchase #5	$86.31	6.806%	$92.1843	$92.18	$92.20	$92.20
Purchase #6	$81.52	10.149%	$89.7935	$89.79	$89.80	$89.80
Purchase #7	$148.39	5.523%	$156.5856	$156.59	$156.60	$156.60
7 purchase totals =	$898.87		$959.5789	$959.57	$959.60	$959.60