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	$136.78	13.864%	$155.7432	$155.74	$155.75	$155.70
Purchase #2	$14.41	9.842%	$15.8282	$15.83	$15.85	$15.80
Purchase #3	$138.30	4.407%	$144.3949	$144.39	$144.40	$144.40
Purchase #4	$209.93	6.162%	$222.8659	$222.87	$222.85	$222.90
Purchase #5	$19.85	11.607%	$22.154	$22.15	$22.15	$22.20
Purchase #6	$44.98	6.271%	$47.8007	$47.80	$47.80	$47.80
Purchase #7	$48.53	6.778%	$51.8194	$51.82	$51.80	$51.80
7 purchase totals =	$612.78		$660.6063	$660.60	$660.60	$660.60