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	$48.94	13.634%	$55.6125	$55.61	$55.60	$55.60
Purchase #2	$57.90	12.808%	$65.3158	$65.32	$65.30	$65.30
Purchase #3	$134.62	10.528%	$148.7928	$148.79	$148.80	$148.80
Purchase #4	$75.25	4.822%	$78.8786	$78.88	$78.90	$78.90
Purchase #5	$54.44	12.510%	$61.2504	$61.25	$61.25	$61.30
Purchase #6	$79.83	6.512%	$85.0285	$85.03	$85.05	$85.00
Purchase #7	$86.26	13.327%	$97.7559	$97.76	$97.75	$97.80
7 purchase totals =	$537.24		$592.6345	$592.64	$592.65	$592.70