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	$100.82	7.147%	$108.0256	$108.03	$108.05	$108.00
Purchase #2	$125.44	5.620%	$132.4897	$132.49	$132.50	$132.50
Purchase #3	$110.35	12.253%	$123.8712	$123.87	$123.85	$123.90
Purchase #4	$9.36	13.659%	$10.6385	$10.64	$10.65	$10.60
Purchase #5	$9.90	5.815%	$10.4757	$10.48	$10.50	$10.50
Purchase #6	$41.69	8.239%	$45.1248	$45.12	$45.10	$45.10
Purchase #7	$97.53	4.750%	$102.1627	$102.16	$102.15	$102.20
7 purchase totals =	$495.09		$532.7882	$532.79	$532.80	$532.80