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	$50.55	11.687%	$56.4578	$56.46	$56.45	$56.50
Purchase #2	$104.75	6.562%	$111.6237	$111.62	$111.60	$111.60
Purchase #3	$12.53	11.395%	$13.9578	$13.96	$13.95	$14.00
Purchase #4	$117.27	6.288%	$124.6439	$124.64	$124.65	$124.60
Purchase #5	$18.29	11.404%	$20.3758	$20.38	$20.40	$20.40
Purchase #6	$42.72	12.264%	$47.9592	$47.96	$47.95	$48.00
Purchase #7	$247.80	13.564%	$281.4116	$281.41	$281.40	$281.40
7 purchase totals =	$593.91		$656.4298	$656.43	$656.40	$656.50