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	$52.27	10.389%	$57.7003	$57.70	$57.70	$57.70
Purchase #2	$76.82	6.666%	$81.9408	$81.94	$81.95	$81.90
Purchase #3	$54.57	12.311%	$61.2881	$61.29	$61.30	$61.30
Purchase #4	$52.48	3.833%	$54.4916	$54.49	$54.50	$54.50
Purchase #5	$242.28	13.435%	$274.8303	$274.83	$274.85	$274.80
Purchase #6	$67.86	4.687%	$71.0406	$71.04	$71.05	$71.00
Purchase #7	$228.58	10.474%	$252.5215	$252.52	$252.50	$252.50
7 purchase totals =	$774.86		$853.8132	$853.81	$853.85	$853.70