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	$237.50	11.754%	$265.4158	$265.42	$265.40	$265.40
Purchase #2	$17.80	6.207%	$18.9048	$18.90	$18.90	$18.90
Purchase #3	$31.40	13.305%	$35.5778	$35.58	$35.60	$35.60
Purchase #4	$34.89	8.413%	$37.8253	$37.83	$37.85	$37.80
Purchase #5	$37.67	9.160%	$41.1206	$41.12	$41.10	$41.10
Purchase #6	$60.79	10.578%	$67.2204	$67.22	$67.20	$67.20
Purchase #7	$52.87	5.557%	$55.808	$55.81	$55.80	$55.80
7 purchase totals =	$472.92		$521.8727	$521.88	$521.85	$521.80