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	$205.69	4.165%	$214.257	$214.26	$214.25	$214.30
Purchase #2	$231.82	12.319%	$260.3779	$260.38	$260.40	$260.40
Purchase #3	$90.98	8.619%	$98.8216	$98.82	$98.80	$98.80
Purchase #4	$145.59	4.509%	$152.1547	$152.15	$152.15	$152.20
Purchase #5	$99.85	12.278%	$112.1096	$112.11	$112.10	$112.10
Purchase #6	$237.30	8.139%	$256.6138	$256.61	$256.60	$256.60
Purchase #7	$132.81	3.399%	$137.3242	$137.32	$137.30	$137.30
7 purchase totals =	$1,144.04		$1,231.6588	$1,231.65	$1,231.60	$1,231.70