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	$82.99	8.568%	$90.1006	$90.10	$90.10	$90.10
Purchase #2	$98.76	5.598%	$104.2886	$104.29	$104.30	$104.30
Purchase #3	$35.38	10.788%	$39.1968	$39.20	$39.20	$39.20
Purchase #4	$15.75	13.209%	$17.8304	$17.83	$17.85	$17.80
Purchase #5	$179.87	5.673%	$190.074	$190.07	$190.05	$190.10
Purchase #6	$189.78	5.233%	$199.7112	$199.71	$199.70	$199.70
Purchase #7	$173.29	3.523%	$179.395	$179.40	$179.40	$179.40
7 purchase totals =	$775.82		$820.5966	$820.60	$820.60	$820.60