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	$102.84	3.828%	$106.7767	$106.78	$106.80	$106.80
Purchase #2	$136.47	3.365%	$141.0622	$141.06	$141.05	$141.10
Purchase #3	$118.93	3.520%	$123.1163	$123.12	$123.10	$123.10
Purchase #4	$137.77	8.754%	$149.8304	$149.83	$149.85	$149.80
Purchase #5	$154.26	12.389%	$173.3713	$173.37	$173.35	$173.40
Purchase #6	$40.75	4.533%	$42.5972	$42.60	$42.60	$42.60
Purchase #7	$159.27	7.821%	$171.7265	$171.73	$171.75	$171.70
7 purchase totals =	$850.29		$908.4806	$908.49	$908.50	$908.50