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	$59.54	13.143%	$67.3653	$67.37	$67.35	$67.40
Purchase #2	$69.60	12.389%	$78.2227	$78.22	$78.20	$78.20
Purchase #3	$184.78	3.626%	$191.4801	$191.48	$191.50	$191.50
Purchase #4	$194.46	5.813%	$205.764	$205.76	$205.75	$205.80
Purchase #5	$46.51	10.214%	$51.2605	$51.26	$51.25	$51.30
Purchase #6	$57.62	9.860%	$63.3013	$63.30	$63.30	$63.30
Purchase #7	$15.27	12.244%	$17.1397	$17.14	$17.15	$17.10
7 purchase totals =	$627.78		$674.5336	$674.53	$674.50	$674.60