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	$244.44	8.338%	$264.8214	$264.82	$264.80	$264.80
Purchase #2	$57.27	7.434%	$61.5275	$61.53	$61.55	$61.50
Purchase #3	$26.46	12.814%	$29.8506	$29.85	$29.85	$29.90
Purchase #4	$65.79	10.232%	$72.5216	$72.52	$72.50	$72.50
Purchase #5	$30.74	5.144%	$32.3213	$32.32	$32.30	$32.30
Purchase #6	$91.67	10.385%	$101.1899	$101.19	$101.20	$101.20
Purchase #7	$56.65	6.777%	$60.4892	$60.49	$60.50	$60.50
7 purchase totals =	$573.02		$622.7215	$622.72	$622.70	$622.70