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	$80.30	13.348%	$91.0184	$91.02	$91.00	$91.00
Purchase #2	$146.30	10.476%	$161.6264	$161.63	$161.65	$161.60
Purchase #3	$63.98	10.656%	$70.7977	$70.80	$70.80	$70.80
Purchase #4	$91.66	12.782%	$103.376	$103.38	$103.40	$103.40
Purchase #5	$112.30	13.582%	$127.5526	$127.55	$127.55	$127.60
Purchase #6	$250.52	5.332%	$263.8777	$263.88	$263.90	$263.90
Purchase #7	$104.32	6.829%	$111.444	$111.44	$111.45	$111.40
7 purchase totals =	$849.38		$929.6928	$929.70	$929.75	$929.70