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	$235.46	6.383%	$250.4894	$250.49	$250.50	$250.50
Purchase #2	$37.33	6.233%	$39.6568	$39.66	$39.65	$39.70
Purchase #3	$12.78	4.338%	$13.3344	$13.33	$13.35	$13.30
Purchase #4	$41.84	6.460%	$44.5429	$44.54	$44.55	$44.50
Purchase #5	$39.46	12.737%	$44.486	$44.49	$44.50	$44.50
Purchase #6	$238.71	7.132%	$255.7348	$255.73	$255.75	$255.70
Purchase #7	$182.52	4.544%	$190.8137	$190.81	$190.80	$190.80
7 purchase totals =	$788.10		$839.0580	$839.05	$839.10	$839.00