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	$126.59	6.222%	$134.4664	$134.47	$134.45	$134.50
Purchase #2	$224.29	6.240%	$238.2857	$238.29	$238.30	$238.30
Purchase #3	$67.98	6.689%	$72.5272	$72.53	$72.55	$72.50
Purchase #4	$18.52	4.302%	$19.3167	$19.32	$19.30	$19.30
Purchase #5	$50.59	11.249%	$56.2809	$56.28	$56.30	$56.30
Purchase #6	$199.62	12.233%	$224.0395	$224.04	$224.05	$224.00
Purchase #7	$87.45	8.298%	$94.7066	$94.71	$94.70	$94.70
7 purchase totals =	$775.04		$839.6230	$839.64	$839.65	$839.60