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	$79.43	13.617%	$90.246	$90.25	$90.25	$90.20
Purchase #2	$10.97	8.621%	$11.9157	$11.92	$11.90	$11.90
Purchase #3	$52.47	12.199%	$58.8708	$58.87	$58.85	$58.90
Purchase #4	$29.86	5.131%	$31.3921	$31.39	$31.40	$31.40
Purchase #5	$59.53	12.249%	$66.8218	$66.82	$66.80	$66.80
Purchase #6	$229.47	13.243%	$259.8587	$259.86	$259.85	$259.90
Purchase #7	$17.39	9.760%	$19.0873	$19.09	$19.10	$19.10
7 purchase totals =	$479.12		$538.1924	$538.20	$538.15	$538.20