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	$10.39	13.734%	$11.817	$11.82	$11.80	$11.80
Purchase #2	$111.54	4.687%	$116.7679	$116.77	$116.75	$116.80
Purchase #3	$138.27	5.471%	$145.8348	$145.83	$145.85	$145.80
Purchase #4	$87.68	4.148%	$91.317	$91.32	$91.30	$91.30
Purchase #5	$77.65	4.711%	$81.3081	$81.31	$81.30	$81.30
Purchase #6	$100.80	4.839%	$105.6777	$105.68	$105.70	$105.70
Purchase #7	$168.72	11.300%	$187.7854	$187.79	$187.80	$187.80
7 purchase totals =	$695.05		$740.5079	$740.52	$740.50	$740.50