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	$71.66	8.397%	$77.6773	$77.68	$77.70	$77.70
Purchase #2	$36.77	11.720%	$41.0794	$41.08	$41.10	$41.10
Purchase #3	$153.47	12.605%	$172.8149	$172.81	$172.80	$172.80
Purchase #4	$174.98	6.808%	$186.8926	$186.89	$186.90	$186.90
Purchase #5	$45.75	3.279%	$47.2501	$47.25	$47.25	$47.30
Purchase #6	$182.70	7.610%	$196.6035	$196.60	$196.60	$196.60
Purchase #7	$146.83	8.278%	$158.9846	$158.98	$159.00	$159.00
7 purchase totals =	$812.16		$881.3024	$881.29	$881.35	$881.40