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	$129.57	7.408%	$139.1685	$139.17	$139.15	$139.20
Purchase #2	$139.25	12.379%	$156.4878	$156.49	$156.50	$156.50
Purchase #3	$15.85	11.457%	$17.6659	$17.67	$17.65	$17.70
Purchase #4	$91.41	10.157%	$100.6945	$100.69	$100.70	$100.70
Purchase #5	$30.89	8.592%	$33.5441	$33.54	$33.55	$33.50
Purchase #6	$11.41	10.834%	$12.6462	$12.65	$12.65	$12.60
Purchase #7	$59.85	5.182%	$62.9514	$62.95	$62.95	$63.00
7 purchase totals =	$478.23		$523.1584	$523.16	$523.15	$523.20