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	$56.59	4.650%	$59.2214	$59.22	$59.20	$59.20
Purchase #2	$207.88	12.130%	$233.0958	$233.10	$233.10	$233.10
Purchase #3	$122.77	3.744%	$127.3665	$127.37	$127.35	$127.40
Purchase #4	$70.99	5.468%	$74.8717	$74.87	$74.85	$74.90
Purchase #5	$103.71	13.279%	$117.4817	$117.48	$117.50	$117.50
Purchase #6	$10.72	5.640%	$11.3246	$11.32	$11.30	$11.30
Purchase #7	$183.89	13.367%	$208.4706	$208.47	$208.45	$208.50
7 purchase totals =	$756.55		$831.8323	$831.83	$831.75	$831.90