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	$26.38	12.210%	$29.601	$29.60	$29.60	$29.60
Purchase #2	$185.47	8.106%	$200.5042	$200.50	$200.50	$200.50
Purchase #3	$116.28	6.186%	$123.4731	$123.47	$123.45	$123.50
Purchase #4	$113.73	9.758%	$124.8278	$124.83	$124.85	$124.80
Purchase #5	$65.86	7.865%	$71.0399	$71.04	$71.05	$71.00
Purchase #6	$192.92	5.267%	$203.0811	$203.08	$203.10	$203.10
Purchase #7	$50.93	10.495%	$56.2751	$56.28	$56.30	$56.30
7 purchase totals =	$751.57		$808.8022	$808.80	$808.85	$808.80