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	$29.97	11.526%	$33.4243	$33.42	$33.40	$33.40
Purchase #2	$162.33	8.238%	$175.7027	$175.70	$175.70	$175.70
Purchase #3	$112.82	9.230%	$123.2333	$123.23	$123.25	$123.20
Purchase #4	$58.72	4.654%	$61.4528	$61.45	$61.45	$61.50
Purchase #5	$168.66	13.782%	$191.9047	$191.90	$191.90	$191.90
Purchase #6	$94.64	6.588%	$100.8749	$100.87	$100.85	$100.90
Purchase #7	$249.99	9.123%	$272.7966	$272.80	$272.80	$272.80
7 purchase totals =	$877.13		$959.3893	$959.37	$959.35	$959.40