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	$134.80	10.127%	$148.4512	$148.45	$148.45	$148.50
Purchase #2	$20.72	9.190%	$22.6242	$22.62	$22.60	$22.60
Purchase #3	$38.94	9.825%	$42.7659	$42.77	$42.75	$42.80
Purchase #4	$93.55	12.545%	$105.2858	$105.29	$105.30	$105.30
Purchase #5	$231.83	11.228%	$257.8599	$257.86	$257.85	$257.90
Purchase #6	$33.81	4.288%	$35.2598	$35.26	$35.25	$35.30
Purchase #7	$64.28	6.560%	$68.4968	$68.50	$68.50	$68.50
7 purchase totals =	$617.93		$680.7436	$680.75	$680.70	$680.90