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	$43.83	10.693%	$48.5167	$48.52	$48.50	$48.50
Purchase #2	$73.26	11.694%	$81.827	$81.83	$81.85	$81.80
Purchase #3	$213.73	5.388%	$225.2458	$225.25	$225.25	$225.20
Purchase #4	$41.55	9.287%	$45.4087	$45.41	$45.40	$45.40
Purchase #5	$82.77	9.813%	$90.8922	$90.89	$90.90	$90.90
Purchase #6	$148.61	10.835%	$164.7119	$164.71	$164.70	$164.70
Purchase #7	$242.32	5.224%	$254.9788	$254.98	$255.00	$255.00
7 purchase totals =	$846.07		$911.5811	$911.59	$911.60	$911.50