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	$74.68	4.673%	$78.1698	$78.17	$78.15	$78.20
Purchase #2	$125.39	4.158%	$130.6037	$130.60	$130.60	$130.60
Purchase #3	$116.40	5.722%	$123.0604	$123.06	$123.05	$123.10
Purchase #4	$51.78	11.635%	$57.8046	$57.80	$57.80	$57.80
Purchase #5	$236.92	10.115%	$260.8845	$260.88	$260.90	$260.90
Purchase #6	$211.97	8.341%	$229.6504	$229.65	$229.65	$229.70
Purchase #7	$94.67	11.854%	$105.8922	$105.89	$105.90	$105.90
7 purchase totals =	$911.81		$986.0656	$986.05	$986.05	$986.20