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	$85.51	4.659%	$89.4939	$89.49	$89.50	$89.50
Purchase #2	$97.87	7.443%	$105.1545	$105.15	$105.15	$105.20
Purchase #3	$137.52	6.781%	$146.8452	$146.85	$146.85	$146.80
Purchase #4	$164.43	6.255%	$174.7151	$174.72	$174.70	$174.70
Purchase #5	$205.26	9.528%	$224.8172	$224.82	$224.80	$224.80
Purchase #6	$135.30	3.160%	$139.5755	$139.58	$139.60	$139.60
Purchase #7	$15.71	5.611%	$16.5915	$16.59	$16.60	$16.60
7 purchase totals =	$841.60		$897.1929	$897.20	$897.20	$897.20