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	$102.34	6.381%	$108.8703	$108.87	$108.85	$108.90
Purchase #2	$132.58	10.145%	$146.0302	$146.03	$146.05	$146.00
Purchase #3	$238.42	8.311%	$258.2351	$258.24	$258.25	$258.20
Purchase #4	$180.41	8.686%	$196.0804	$196.08	$196.10	$196.10
Purchase #5	$17.44	4.553%	$18.234	$18.23	$18.25	$18.20
Purchase #6	$93.69	10.706%	$103.7205	$103.72	$103.70	$103.70
Purchase #7	$27.84	4.452%	$29.0794	$29.08	$29.10	$29.10
7 purchase totals =	$792.72		$860.2499	$860.25	$860.30	$860.20