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	$107.47	8.115%	$116.1912	$116.19	$116.20	$116.20
Purchase #2	$222.63	11.765%	$248.8224	$248.82	$248.80	$248.80
Purchase #3	$74.78	9.150%	$81.6224	$81.62	$81.60	$81.60
Purchase #4	$67.25	7.474%	$72.2763	$72.28	$72.30	$72.30
Purchase #5	$145.89	7.707%	$157.1337	$157.13	$157.15	$157.10
Purchase #6	$248.25	3.138%	$256.0401	$256.04	$256.05	$256.00
Purchase #7	$126.56	8.632%	$137.4847	$137.48	$137.50	$137.50
7 purchase totals =	$992.83		$1,069.5708	$1,069.56	$1,069.60	$1,069.50