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	$16.51	7.573%	$17.7603	$17.76	$17.75	$17.80
Purchase #2	$7.62	13.285%	$8.6323	$8.63	$8.65	$8.60
Purchase #3	$138.69	7.209%	$148.6882	$148.69	$148.70	$148.70
Purchase #4	$56.64	4.407%	$59.1361	$59.14	$59.15	$59.10
Purchase #5	$146.91	8.310%	$159.1182	$159.12	$159.10	$159.10
Purchase #6	$63.66	13.380%	$72.1777	$72.18	$72.20	$72.20
Purchase #7	$71.63	9.388%	$78.3546	$78.35	$78.35	$78.40
7 purchase totals =	$501.66		$543.8674	$543.87	$543.90	$543.90