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	$46.79	6.541%	$49.8505	$49.85	$49.85	$49.90
Purchase #2	$224.43	10.240%	$247.4116	$247.41	$247.40	$247.40
Purchase #3	$174.81	8.210%	$189.1619	$189.16	$189.15	$189.20
Purchase #4	$90.82	10.330%	$100.2017	$100.20	$100.20	$100.20
Purchase #5	$116.91	5.724%	$123.6019	$123.60	$123.60	$123.60
Purchase #6	$78.72	10.444%	$86.9415	$86.94	$86.95	$86.90
Purchase #7	$60.79	11.388%	$67.7128	$67.71	$67.70	$67.70
7 purchase totals =	$793.27		$864.8819	$864.87	$864.85	$864.90