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	$142.67	9.540%	$156.2807	$156.28	$156.30	$156.30
Purchase #2	$166.59	4.296%	$173.7467	$173.75	$173.75	$173.70
Purchase #3	$133.70	4.624%	$139.8823	$139.88	$139.90	$139.90
Purchase #4	$39.45	4.290%	$41.1424	$41.14	$41.15	$41.10
Purchase #5	$89.48	12.102%	$100.3089	$100.31	$100.30	$100.30
Purchase #6	$160.30	3.522%	$165.9458	$165.95	$165.95	$165.90
Purchase #7	$214.86	6.104%	$227.9751	$227.98	$228.00	$228.00
7 purchase totals =	$947.05		$1,005.2819	$1,005.29	$1,005.35	$1,005.20