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	$87.72	4.443%	$91.6174	$91.62	$91.60	$91.60
Purchase #2	$110.50	5.479%	$116.5543	$116.55	$116.55	$116.60
Purchase #3	$112.25	10.178%	$123.6748	$123.67	$123.65	$123.70
Purchase #4	$45.90	8.589%	$49.8424	$49.84	$49.85	$49.80
Purchase #5	$124.49	3.296%	$128.5932	$128.59	$128.60	$128.60
Purchase #6	$95.42	13.407%	$108.213	$108.21	$108.20	$108.20
Purchase #7	$67.90	5.826%	$71.8559	$71.86	$71.85	$71.90
7 purchase totals =	$644.18		$690.3510	$690.34	$690.30	$690.40