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	$49.49	12.117%	$55.4867	$55.49	$55.50	$55.50
Purchase #2	$101.85	7.365%	$109.3513	$109.35	$109.35	$109.40
Purchase #3	$35.72	7.531%	$38.4101	$38.41	$38.40	$38.40
Purchase #4	$54.86	8.492%	$59.5187	$59.52	$59.50	$59.50
Purchase #5	$12.28	8.861%	$13.3681	$13.37	$13.35	$13.40
Purchase #6	$68.30	8.844%	$74.3405	$74.34	$74.35	$74.30
Purchase #7	$104.41	11.123%	$116.0235	$116.02	$116.00	$116.00
7 purchase totals =	$426.91		$466.4989	$466.50	$466.45	$466.50