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	$42.70	11.647%	$47.6733	$47.67	$47.65	$47.70
Purchase #2	$248.60	12.356%	$279.317	$279.32	$279.30	$279.30
Purchase #3	$131.28	8.362%	$142.2576	$142.26	$142.25	$142.30
Purchase #4	$47.71	13.524%	$54.1623	$54.16	$54.15	$54.20
Purchase #5	$146.52	4.301%	$152.8218	$152.82	$152.80	$152.80
Purchase #6	$55.29	13.493%	$62.7503	$62.75	$62.75	$62.80
Purchase #7	$227.72	5.136%	$239.4157	$239.42	$239.40	$239.40
7 purchase totals =	$899.82		$978.3980	$978.40	$978.30	$978.50