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	$94.39	6.128%	$100.1742	$100.17	$100.15	$100.20
Purchase #2	$149.60	3.519%	$154.8644	$154.86	$154.85	$154.90
Purchase #3	$42.74	10.343%	$47.1606	$47.16	$47.15	$47.20
Purchase #4	$41.79	9.569%	$45.7889	$45.79	$45.80	$45.80
Purchase #5	$122.62	10.292%	$135.2401	$135.24	$135.25	$135.20
Purchase #6	$69.60	4.772%	$72.9213	$72.92	$72.90	$72.90
Purchase #7	$102.40	9.287%	$111.9099	$111.91	$111.90	$111.90
7 purchase totals =	$623.14		$668.0594	$668.05	$668.00	$668.10