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	$19.89	4.105%	$20.7065	$20.71	$20.70	$20.70
Purchase #2	$38.26	8.255%	$41.4184	$41.42	$41.40	$41.40
Purchase #3	$29.54	10.162%	$32.5419	$32.54	$32.55	$32.50
Purchase #4	$80.96	13.784%	$92.1195	$92.12	$92.10	$92.10
Purchase #5	$64.73	8.185%	$70.0282	$70.03	$70.05	$70.00
Purchase #6	$134.58	9.560%	$147.4458	$147.45	$147.45	$147.40
Purchase #7	$116.41	5.867%	$123.2398	$123.24	$123.25	$123.20
7 purchase totals =	$484.37		$527.5001	$527.51	$527.50	$527.30