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	$112.52	3.262%	$116.1904	$116.19	$116.20	$116.20
Purchase #2	$95.41	4.324%	$99.5355	$99.54	$99.55	$99.50
Purchase #3	$72.98	10.255%	$80.4641	$80.46	$80.45	$80.50
Purchase #4	$172.51	6.310%	$183.3954	$183.40	$183.40	$183.40
Purchase #5	$107.78	7.869%	$116.2612	$116.26	$116.25	$116.30
Purchase #6	$158.59	8.599%	$172.2272	$172.23	$172.25	$172.20
Purchase #7	$130.99	10.287%	$144.4649	$144.46	$144.45	$144.50
7 purchase totals =	$850.78		$912.5387	$912.54	$912.55	$912.60