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	$58.35	12.858%	$65.8526	$65.85	$65.85	$65.90
Purchase #2	$107.45	3.557%	$111.272	$111.27	$111.25	$111.30
Purchase #3	$16.70	7.842%	$18.0096	$18.01	$18.00	$18.00
Purchase #4	$242.57	11.839%	$271.2879	$271.29	$271.30	$271.30
Purchase #5	$70.59	4.162%	$73.528	$73.53	$73.55	$73.50
Purchase #6	$144.66	7.332%	$155.2665	$155.27	$155.25	$155.30
Purchase #7	$62.33	13.103%	$70.4971	$70.50	$70.50	$70.50
7 purchase totals =	$702.65		$765.7137	$765.72	$765.70	$765.80