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	$73.53	5.786%	$77.7844	$77.78	$77.80	$77.80
Purchase #2	$215.86	7.282%	$231.5789	$231.58	$231.60	$231.60
Purchase #3	$90.69	11.103%	$100.7593	$100.76	$100.75	$100.80
Purchase #4	$71.72	9.357%	$78.4308	$78.43	$78.45	$78.40
Purchase #5	$97.62	13.831%	$111.1218	$111.12	$111.10	$111.10
Purchase #6	$42.88	7.586%	$46.1329	$46.13	$46.15	$46.10
Purchase #7	$127.63	10.664%	$141.2405	$141.24	$141.25	$141.20
7 purchase totals =	$719.93		$787.0486	$787.04	$787.10	$787.00