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	$95.64	13.440%	$108.494	$108.49	$108.50	$108.50
Purchase #2	$37.76	3.172%	$38.9577	$38.96	$38.95	$39.00
Purchase #3	$162.35	11.544%	$181.0917	$181.09	$181.10	$181.10
Purchase #4	$85.71	8.136%	$92.6834	$92.68	$92.70	$92.70
Purchase #5	$38.76	5.345%	$40.8317	$40.83	$40.85	$40.80
Purchase #6	$177.45	7.812%	$191.3124	$191.31	$191.30	$191.30
Purchase #7	$146.48	12.354%	$164.5761	$164.58	$164.60	$164.60
7 purchase totals =	$744.15		$817.9470	$817.94	$818.00	$818.00