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	$234.46	3.380%	$242.3847	$242.38	$242.40	$242.40
Purchase #2	$97.56	13.166%	$110.4047	$110.40	$110.40	$110.40
Purchase #3	$142.26	9.301%	$155.4916	$155.49	$155.50	$155.50
Purchase #4	$126.76	10.147%	$139.6223	$139.62	$139.60	$139.60
Purchase #5	$45.87	10.652%	$50.7561	$50.76	$50.75	$50.80
Purchase #6	$205.93	9.525%	$225.5448	$225.54	$225.55	$225.50
Purchase #7	$244.61	4.617%	$255.9036	$255.90	$255.90	$255.90
7 purchase totals =	$1,097.45		$1,180.1078	$1,180.09	$1,180.10	$1,180.10