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	$54.46	11.255%	$60.5895	$60.59	$60.60	$60.60
Purchase #2	$51.84	10.551%	$57.3096	$57.31	$57.30	$57.30
Purchase #3	$227.63	12.646%	$256.4161	$256.42	$256.40	$256.40
Purchase #4	$244.52	11.104%	$271.6715	$271.67	$271.65	$271.70
Purchase #5	$81.56	9.634%	$89.4175	$89.42	$89.40	$89.40
Purchase #6	$120.63	3.726%	$125.1247	$125.12	$125.10	$125.10
Purchase #7	$19.66	9.181%	$21.465	$21.47	$21.45	$21.50
7 purchase totals =	$800.30		$881.9939	$882.00	$881.90	$882.00