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	$49.62	11.742%	$55.4464	$55.45	$55.45	$55.40
Purchase #2	$117.56	3.714%	$121.9262	$121.93	$121.95	$121.90
Purchase #3	$111.37	13.563%	$126.4751	$126.48	$126.50	$126.50
Purchase #4	$28.89	5.436%	$30.4605	$30.46	$30.45	$30.50
Purchase #5	$52.91	10.299%	$58.3592	$58.36	$58.35	$58.40
Purchase #6	$78.69	8.629%	$85.4802	$85.48	$85.50	$85.50
Purchase #7	$92.85	7.179%	$99.5157	$99.52	$99.50	$99.50
7 purchase totals =	$531.89		$577.6633	$577.68	$577.70	$577.70