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	$146.66	12.119%	$164.4337	$164.43	$164.45	$164.40
Purchase #2	$157.96	9.390%	$172.7924	$172.79	$172.80	$172.80
Purchase #3	$219.53	6.400%	$233.5799	$233.58	$233.60	$233.60
Purchase #4	$16.34	12.597%	$18.3983	$18.40	$18.40	$18.40
Purchase #5	$45.74	8.528%	$49.6407	$49.64	$49.65	$49.60
Purchase #6	$126.54	12.748%	$142.6713	$142.67	$142.65	$142.70
Purchase #7	$126.27	10.321%	$139.3023	$139.30	$139.30	$139.30
7 purchase totals =	$839.04		$920.8186	$920.81	$920.85	$920.80