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	$136.41	8.784%	$148.3923	$148.39	$148.40	$148.40
Purchase #2	$20.94	12.727%	$23.605	$23.61	$23.60	$23.60
Purchase #3	$82.80	8.858%	$90.1344	$90.13	$90.15	$90.10
Purchase #4	$52.78	12.660%	$59.4619	$59.46	$59.45	$59.50
Purchase #5	$38.70	13.496%	$43.923	$43.92	$43.90	$43.90
Purchase #6	$144.82	10.452%	$159.9566	$159.96	$159.95	$160.00
Purchase #7	$124.77	4.585%	$130.4907	$130.49	$130.50	$130.50
7 purchase totals =	$601.22		$655.9639	$655.96	$655.95	$656.00