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	$17.49	13.137%	$19.7877	$19.79	$19.80	$19.80
Purchase #2	$223.96	13.873%	$255.03	$255.03	$255.05	$255.00
Purchase #3	$156.34	7.636%	$168.2781	$168.28	$168.30	$168.30
Purchase #4	$19.52	9.783%	$21.4296	$21.43	$21.45	$21.40
Purchase #5	$78.70	12.833%	$88.7996	$88.80	$88.80	$88.80
Purchase #6	$126.43	8.573%	$137.2688	$137.27	$137.25	$137.30
Purchase #7	$35.37	5.680%	$37.379	$37.38	$37.40	$37.40
7 purchase totals =	$657.81		$727.9728	$727.98	$728.05	$728.00