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	$155.78	5.405%	$164.1999	$164.20	$164.20	$164.20
Purchase #2	$45.68	8.716%	$49.6615	$49.66	$49.65	$49.70
Purchase #3	$104.94	11.103%	$116.5915	$116.59	$116.60	$116.60
Purchase #4	$118.44	3.848%	$122.9976	$123.00	$123.00	$123.00
Purchase #5	$98.63	7.318%	$105.8477	$105.85	$105.85	$105.80
Purchase #6	$40.41	4.616%	$42.2753	$42.28	$42.30	$42.30
Purchase #7	$35.66	10.256%	$39.3173	$39.32	$39.30	$39.30
7 purchase totals =	$599.54		$640.8908	$640.90	$640.90	$640.90