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	$60.33	10.867%	$66.8861	$66.89	$66.90	$66.90
Purchase #2	$207.59	8.345%	$224.9134	$224.91	$224.90	$224.90
Purchase #3	$86.52	3.672%	$89.697	$89.70	$89.70	$89.70
Purchase #4	$77.38	13.118%	$87.5307	$87.53	$87.55	$87.50
Purchase #5	$158.65	13.156%	$179.522	$179.52	$179.50	$179.50
Purchase #6	$18.62	4.713%	$19.4976	$19.50	$19.50	$19.50
Purchase #7	$21.71	11.685%	$24.2468	$24.25	$24.25	$24.20
7 purchase totals =	$630.80		$692.2936	$692.30	$692.30	$692.20