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	$226.34	4.837%	$237.2881	$237.29	$237.30	$237.30
Purchase #2	$111.72	10.560%	$123.5176	$123.52	$123.50	$123.50
Purchase #3	$31.46	8.585%	$34.1608	$34.16	$34.15	$34.20
Purchase #4	$173.80	9.738%	$190.7246	$190.72	$190.70	$190.70
Purchase #5	$241.37	10.303%	$266.2384	$266.24	$266.25	$266.20
Purchase #6	$59.59	10.767%	$66.0061	$66.01	$66.00	$66.00
Purchase #7	$16.96	9.591%	$18.5866	$18.59	$18.60	$18.60
7 purchase totals =	$861.24		$936.5222	$936.53	$936.50	$936.50