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	$107.83	4.381%	$112.554	$112.55	$112.55	$112.60
Purchase #2	$123.57	13.117%	$139.7787	$139.78	$139.80	$139.80
Purchase #3	$6.29	10.804%	$6.9696	$6.97	$6.95	$7.00
Purchase #4	$89.27	5.487%	$94.1682	$94.17	$94.15	$94.20
Purchase #5	$127.50	3.133%	$131.4946	$131.49	$131.50	$131.50
Purchase #6	$50.90	13.815%	$57.9318	$57.93	$57.95	$57.90
Purchase #7	$22.90	8.142%	$24.7645	$24.76	$24.75	$24.80
7 purchase totals =	$528.26		$567.6614	$567.65	$567.65	$567.80