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	$220.70	9.798%	$242.3242	$242.32	$242.30	$242.30
Purchase #2	$39.80	7.178%	$42.6568	$42.66	$42.65	$42.70
Purchase #3	$192.42	6.294%	$204.5309	$204.53	$204.55	$204.50
Purchase #4	$101.62	11.622%	$113.4303	$113.43	$113.45	$113.40
Purchase #5	$79.65	13.461%	$90.3717	$90.37	$90.35	$90.40
Purchase #6	$63.57	8.265%	$68.8241	$68.82	$68.80	$68.80
Purchase #7	$232.33	9.547%	$254.5105	$254.51	$254.50	$254.50
7 purchase totals =	$930.09		$1,016.6485	$1,016.64	$1,016.60	$1,016.60