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	$97.98	5.208%	$103.0828	$103.08	$103.10	$103.10
Purchase #2	$19.59	11.425%	$21.8282	$21.83	$21.85	$21.80
Purchase #3	$181.47	10.415%	$200.3701	$200.37	$200.35	$200.40
Purchase #4	$14.68	8.738%	$15.9627	$15.96	$15.95	$16.00
Purchase #5	$37.62	4.381%	$39.2681	$39.27	$39.25	$39.30
Purchase #6	$101.93	10.130%	$112.2555	$112.26	$112.25	$112.30
Purchase #7	$36.84	4.826%	$38.6179	$38.62	$38.60	$38.60
7 purchase totals =	$490.11		$531.3853	$531.39	$531.35	$531.50