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	$48.89	3.197%	$50.453	$50.45	$50.45	$50.50
Purchase #2	$219.42	8.277%	$237.5814	$237.58	$237.60	$237.60
Purchase #3	$183.50	9.202%	$200.3857	$200.39	$200.40	$200.40
Purchase #4	$103.56	9.209%	$113.0968	$113.10	$113.10	$113.10
Purchase #5	$188.86	8.691%	$205.2738	$205.27	$205.25	$205.30
Purchase #6	$90.65	10.182%	$99.88	$99.88	$99.90	$99.90
Purchase #7	$41.35	12.194%	$46.3922	$46.39	$46.40	$46.40
7 purchase totals =	$876.23		$953.0629	$953.06	$953.10	$953.20