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	$214.61	12.146%	$240.6765	$240.68	$240.70	$240.70
Purchase #2	$61.25	7.648%	$65.9344	$65.93	$65.95	$65.90
Purchase #3	$114.63	10.357%	$126.5022	$126.50	$126.50	$126.50
Purchase #4	$48.93	3.461%	$50.6235	$50.62	$50.60	$50.60
Purchase #5	$94.64	6.122%	$100.4339	$100.43	$100.45	$100.40
Purchase #6	$199.89	5.787%	$211.4576	$211.46	$211.45	$211.50
Purchase #7	$47.45	3.158%	$48.9485	$48.95	$48.95	$48.90
7 purchase totals =	$781.40		$844.5766	$844.57	$844.60	$844.50