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	$92.98	12.189%	$104.3133	$104.31	$104.30	$104.30
Purchase #2	$55.97	12.271%	$62.8381	$62.84	$62.85	$62.80
Purchase #3	$103.60	9.819%	$113.7725	$113.77	$113.75	$113.80
Purchase #4	$10.39	7.152%	$11.1331	$11.13	$11.15	$11.10
Purchase #5	$103.30	12.744%	$116.4646	$116.46	$116.45	$116.50
Purchase #6	$165.58	11.626%	$184.8303	$184.83	$184.85	$184.80
Purchase #7	$242.60	7.796%	$261.5131	$261.51	$261.50	$261.50
7 purchase totals =	$774.42		$854.8650	$854.85	$854.85	$854.80