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	$92.62	5.427%	$97.6465	$97.65	$97.65	$97.60
Purchase #2	$79.79	13.413%	$90.4922	$90.49	$90.50	$90.50
Purchase #3	$88.26	8.151%	$95.4541	$95.45	$95.45	$95.50
Purchase #4	$78.91	5.601%	$83.3297	$83.33	$83.35	$83.30
Purchase #5	$29.43	4.644%	$30.7967	$30.80	$30.80	$30.80
Purchase #6	$17.96	13.434%	$20.3727	$20.37	$20.35	$20.40
Purchase #7	$108.30	3.181%	$111.745	$111.75	$111.75	$111.70
7 purchase totals =	$495.27		$529.8369	$529.84	$529.85	$529.80