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	$38.69	12.437%	$43.5019	$43.50	$43.50	$43.50
Purchase #2	$82.61	11.246%	$91.9003	$91.90	$91.90	$91.90
Purchase #3	$149.42	10.141%	$164.5727	$164.57	$164.55	$164.60
Purchase #4	$236.69	6.728%	$252.6145	$252.61	$252.60	$252.60
Purchase #5	$16.85	12.511%	$18.9581	$18.96	$18.95	$19.00
Purchase #6	$151.60	4.714%	$158.7464	$158.75	$158.75	$158.70
Purchase #7	$209.80	11.192%	$233.2808	$233.28	$233.30	$233.30
7 purchase totals =	$885.66		$963.5747	$963.57	$963.55	$963.60