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	$213.33	11.844%	$238.5968	$238.60	$238.60	$238.60
Purchase #2	$95.51	10.596%	$105.6302	$105.63	$105.65	$105.60
Purchase #3	$145.91	8.609%	$158.4714	$158.47	$158.45	$158.50
Purchase #4	$182.27	8.525%	$197.8085	$197.81	$197.80	$197.80
Purchase #5	$91.52	9.808%	$100.4963	$100.50	$100.50	$100.50
Purchase #6	$95.98	12.647%	$108.1186	$108.12	$108.10	$108.10
Purchase #7	$56.33	8.756%	$61.2623	$61.26	$61.25	$61.30
7 purchase totals =	$880.85		$970.3841	$970.39	$970.35	$970.40