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	$139.52	11.483%	$155.5411	$155.54	$155.55	$155.50
Purchase #2	$48.26	12.629%	$54.3548	$54.35	$54.35	$54.40
Purchase #3	$8.50	11.593%	$9.4854	$9.49	$9.50	$9.50
Purchase #4	$79.98	13.202%	$90.539	$90.54	$90.55	$90.50
Purchase #5	$132.66	6.553%	$141.3532	$141.35	$141.35	$141.40
Purchase #6	$141.56	5.120%	$148.8079	$148.81	$148.80	$148.80
Purchase #7	$36.43	4.754%	$38.1619	$38.16	$38.15	$38.20
7 purchase totals =	$586.91		$638.2433	$638.24	$638.25	$638.30