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	$249.82	11.838%	$279.3937	$279.39	$279.40	$279.40
Purchase #2	$112.63	3.172%	$116.2026	$116.20	$116.20	$116.20
Purchase #3	$179.39	11.670%	$200.3248	$200.32	$200.30	$200.30
Purchase #4	$86.48	9.682%	$94.853	$94.85	$94.85	$94.90
Purchase #5	$187.66	6.713%	$200.2576	$200.26	$200.25	$200.30
Purchase #6	$235.43	4.103%	$245.0897	$245.09	$245.10	$245.10
Purchase #7	$133.53	8.374%	$144.7118	$144.71	$144.70	$144.70
7 purchase totals =	$1,184.94		$1,280.8332	$1,280.82	$1,280.80	$1,280.90