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	$230.34	12.530%	$259.2016	$259.20	$259.20	$259.20
Purchase #2	$157.45	10.172%	$173.4658	$173.47	$173.45	$173.50
Purchase #3	$63.58	9.382%	$69.5451	$69.55	$69.55	$69.50
Purchase #4	$39.89	4.443%	$41.6623	$41.66	$41.65	$41.70
Purchase #5	$151.61	3.631%	$157.115	$157.12	$157.10	$157.10
Purchase #6	$151.71	11.304%	$168.8593	$168.86	$168.85	$168.90
Purchase #7	$87.37	3.632%	$90.5433	$90.54	$90.55	$90.50
7 purchase totals =	$881.95		$960.3924	$960.40	$960.35	$960.40