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	$177.36	6.814%	$189.4453	$189.45	$189.45	$189.40
Purchase #2	$11.53	8.413%	$12.5	$12.50	$12.50	$12.50
Purchase #3	$178.76	3.812%	$185.5743	$185.57	$185.55	$185.60
Purchase #4	$49.52	3.536%	$51.271	$51.27	$51.25	$51.30
Purchase #5	$175.25	9.257%	$191.4729	$191.47	$191.45	$191.50
Purchase #6	$15.50	10.298%	$17.0962	$17.10	$17.10	$17.10
Purchase #7	$35.65	13.732%	$40.5455	$40.55	$40.55	$40.50
7 purchase totals =	$643.57		$687.9052	$687.91	$687.85	$687.90