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	$108.32	9.758%	$118.8899	$118.89	$118.90	$118.90
Purchase #2	$53.83	3.242%	$55.5752	$55.58	$55.60	$55.60
Purchase #3	$59.93	11.429%	$66.7794	$66.78	$66.80	$66.80
Purchase #4	$34.64	12.788%	$39.0698	$39.07	$39.05	$39.10
Purchase #5	$233.49	7.332%	$250.6095	$250.61	$250.60	$250.60
Purchase #6	$41.38	13.564%	$46.9928	$46.99	$47.00	$47.00
Purchase #7	$247.31	11.356%	$275.3945	$275.39	$275.40	$275.40
7 purchase totals =	$778.90		$853.3111	$853.31	$853.35	$853.40