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	$112.45	8.187%	$121.6563	$121.66	$121.65	$121.70
Purchase #2	$100.62	10.429%	$111.1137	$111.11	$111.10	$111.10
Purchase #3	$34.55	10.305%	$38.1104	$38.11	$38.10	$38.10
Purchase #4	$179.58	9.293%	$196.2684	$196.27	$196.25	$196.30
Purchase #5	$17.99	11.737%	$20.1015	$20.10	$20.10	$20.10
Purchase #6	$26.52	12.839%	$29.9249	$29.92	$29.90	$29.90
Purchase #7	$234.71	5.465%	$247.5369	$247.54	$247.55	$247.50
7 purchase totals =	$706.42		$764.7121	$764.71	$764.65	$764.70