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	$209.57	10.135%	$230.8099	$230.81	$230.80	$230.80
Purchase #2	$38.36	9.734%	$42.094	$42.09	$42.10	$42.10
Purchase #3	$181.40	5.225%	$190.8782	$190.88	$190.90	$190.90
Purchase #4	$226.90	12.582%	$255.4486	$255.45	$255.45	$255.40
Purchase #5	$243.77	10.252%	$268.7613	$268.76	$268.75	$268.80
Purchase #6	$160.87	12.790%	$181.4453	$181.45	$181.45	$181.40
Purchase #7	$116.81	13.527%	$132.6109	$132.61	$132.60	$132.60
7 purchase totals =	$1,177.68		$1,302.0482	$1,302.05	$1,302.05	$1,302.00