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	$16.83	9.794%	$18.4783	$18.48	$18.50	$18.50
Purchase #2	$55.37	9.735%	$60.7603	$60.76	$60.75	$60.80
Purchase #3	$132.98	9.163%	$145.165	$145.17	$145.15	$145.20
Purchase #4	$36.28	10.832%	$40.2098	$40.21	$40.20	$40.20
Purchase #5	$190.39	11.776%	$212.8103	$212.81	$212.80	$212.80
Purchase #6	$74.25	12.152%	$83.2729	$83.27	$83.25	$83.30
Purchase #7	$73.96	13.334%	$83.8218	$83.82	$83.80	$83.80
7 purchase totals =	$580.06		$644.5184	$644.52	$644.45	$644.60