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	$94.75	6.196%	$100.6207	$100.62	$100.60	$100.60
Purchase #2	$18.40	8.473%	$19.959	$19.96	$19.95	$20.00
Purchase #3	$185.85	12.512%	$209.1036	$209.10	$209.10	$209.10
Purchase #4	$169.70	12.233%	$190.4594	$190.46	$190.45	$190.50
Purchase #5	$139.39	8.202%	$150.8228	$150.82	$150.80	$150.80
Purchase #6	$77.48	12.860%	$87.4439	$87.44	$87.45	$87.40
Purchase #7	$141.86	11.606%	$158.3243	$158.32	$158.30	$158.30
7 purchase totals =	$827.43		$916.7337	$916.72	$916.65	$916.70