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	$199.69	12.371%	$224.3936	$224.39	$224.40	$224.40
Purchase #2	$103.94	7.685%	$111.9278	$111.93	$111.95	$111.90
Purchase #3	$159.44	5.838%	$168.7481	$168.75	$168.75	$168.70
Purchase #4	$68.68	3.275%	$70.9293	$70.93	$70.95	$70.90
Purchase #5	$12.27	5.128%	$12.8992	$12.90	$12.90	$12.90
Purchase #6	$168.90	13.198%	$191.1914	$191.19	$191.20	$191.20
Purchase #7	$91.93	7.139%	$98.4929	$98.49	$98.50	$98.50
7 purchase totals =	$804.85		$878.5823	$878.58	$878.65	$878.50