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	$49.58	12.639%	$55.8464	$55.85	$55.85	$55.80
Purchase #2	$63.26	3.344%	$65.3754	$65.38	$65.40	$65.40
Purchase #3	$59.64	13.611%	$67.7576	$67.76	$67.75	$67.80
Purchase #4	$157.53	9.107%	$171.8763	$171.88	$171.90	$171.90
Purchase #5	$118.37	4.234%	$123.3818	$123.38	$123.40	$123.40
Purchase #6	$114.26	6.433%	$121.6103	$121.61	$121.60	$121.60
Purchase #7	$30.60	11.108%	$33.999	$34.00	$34.00	$34.00
7 purchase totals =	$593.24		$639.8468	$639.86	$639.90	$639.90