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	$145.89	11.221%	$162.2603	$162.26	$162.25	$162.30
Purchase #2	$37.34	3.569%	$38.6727	$38.67	$38.65	$38.70
Purchase #3	$233.62	12.344%	$262.4581	$262.46	$262.45	$262.50
Purchase #4	$94.76	11.798%	$105.9398	$105.94	$105.95	$105.90
Purchase #5	$173.65	7.853%	$187.2867	$187.29	$187.30	$187.30
Purchase #6	$90.66	6.739%	$96.7696	$96.77	$96.75	$96.80
Purchase #7	$113.77	11.178%	$126.4872	$126.49	$126.50	$126.50
7 purchase totals =	$889.69		$979.8744	$979.88	$979.85	$980.00