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	$32.81	8.180%	$35.4939	$35.49	$35.50	$35.50
Purchase #2	$133.28	4.637%	$139.4602	$139.46	$139.45	$139.50
Purchase #3	$75.95	8.557%	$82.449	$82.45	$82.45	$82.40
Purchase #4	$160.97	10.857%	$178.4465	$178.45	$178.45	$178.40
Purchase #5	$10.86	5.845%	$11.4948	$11.49	$11.50	$11.50
Purchase #6	$134.82	3.660%	$139.7544	$139.75	$139.75	$139.80
Purchase #7	$195.45	9.127%	$213.2887	$213.29	$213.30	$213.30
7 purchase totals =	$744.14		$800.3875	$800.38	$800.40	$800.40