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	$88.35	6.795%	$94.3534	$94.35	$94.35	$94.40
Purchase #2	$40.53	13.182%	$45.8727	$45.87	$45.85	$45.90
Purchase #3	$221.28	10.493%	$244.4989	$244.50	$244.50	$244.50
Purchase #4	$171.85	9.154%	$187.5811	$187.58	$187.60	$187.60
Purchase #5	$51.87	9.573%	$56.8355	$56.84	$56.85	$56.80
Purchase #6	$144.66	11.253%	$160.9386	$160.94	$160.95	$160.90
Purchase #7	$44.56	9.565%	$48.8222	$48.82	$48.80	$48.80
7 purchase totals =	$763.10		$838.9024	$838.90	$838.90	$838.90