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	$76.75	8.298%	$83.1187	$83.12	$83.10	$83.10
Purchase #2	$221.80	13.439%	$251.6077	$251.61	$251.60	$251.60
Purchase #3	$122.86	4.653%	$128.5767	$128.58	$128.60	$128.60
Purchase #4	$112.40	3.323%	$116.1351	$116.14	$116.15	$116.10
Purchase #5	$92.51	11.793%	$103.4197	$103.42	$103.40	$103.40
Purchase #6	$169.96	9.359%	$185.8666	$185.87	$185.85	$185.90
Purchase #7	$68.67	13.734%	$78.1011	$78.10	$78.10	$78.10
7 purchase totals =	$864.95		$946.8256	$946.84	$946.80	$946.80