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	$127.35	9.130%	$138.9771	$138.98	$139.00	$139.00
Purchase #2	$167.92	3.113%	$173.1473	$173.15	$173.15	$173.10
Purchase #3	$143.31	6.208%	$152.2067	$152.21	$152.20	$152.20
Purchase #4	$126.92	11.550%	$141.5793	$141.58	$141.60	$141.60
Purchase #5	$188.26	5.418%	$198.4599	$198.46	$198.45	$198.50
Purchase #6	$175.46	10.510%	$193.9008	$193.90	$193.90	$193.90
Purchase #7	$95.70	5.349%	$100.819	$100.82	$100.80	$100.80
7 purchase totals =	$1,024.92		$1,099.0901	$1,099.10	$1,099.10	$1,099.10