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	$43.96	5.826%	$46.5211	$46.52	$46.50	$46.50
Purchase #2	$149.87	10.121%	$165.0383	$165.04	$165.05	$165.00
Purchase #3	$45.93	9.555%	$50.3186	$50.32	$50.30	$50.30
Purchase #4	$144.92	13.751%	$164.8479	$164.85	$164.85	$164.80
Purchase #5	$112.87	3.149%	$116.4243	$116.42	$116.40	$116.40
Purchase #6	$177.56	6.153%	$188.4853	$188.49	$188.50	$188.50
Purchase #7	$144.66	9.532%	$158.449	$158.45	$158.45	$158.40
7 purchase totals =	$819.77		$890.0845	$890.09	$890.05	$889.90