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	$182.84	3.685%	$189.5777	$189.58	$189.60	$189.60
Purchase #2	$218.40	3.315%	$225.64	$225.64	$225.65	$225.60
Purchase #3	$149.52	5.710%	$158.0576	$158.06	$158.05	$158.10
Purchase #4	$140.60	4.186%	$146.4855	$146.49	$146.50	$146.50
Purchase #5	$56.59	6.862%	$60.4732	$60.47	$60.45	$60.50
Purchase #6	$92.77	11.809%	$103.7252	$103.73	$103.75	$103.70
Purchase #7	$25.55	11.759%	$28.5544	$28.55	$28.55	$28.60
7 purchase totals =	$866.27		$912.5136	$912.52	$912.55	$912.60