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	$92.88	8.210%	$100.5054	$100.51	$100.50	$100.50
Purchase #2	$40.40	12.388%	$45.4048	$45.40	$45.40	$45.40
Purchase #3	$17.90	8.279%	$19.3819	$19.38	$19.40	$19.40
Purchase #4	$80.74	11.295%	$89.8596	$89.86	$89.85	$89.90
Purchase #5	$106.61	9.141%	$116.3552	$116.36	$116.35	$116.40
Purchase #6	$113.75	7.761%	$122.5781	$122.58	$122.60	$122.60
Purchase #7	$69.52	4.764%	$72.8319	$72.83	$72.85	$72.80
7 purchase totals =	$521.80		$566.9169	$566.92	$566.95	$567.00