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	$130.83	6.771%	$139.6885	$139.69	$139.70	$139.70
Purchase #2	$18.80	13.164%	$21.2748	$21.27	$21.25	$21.30
Purchase #3	$51.80	8.674%	$56.2931	$56.29	$56.30	$56.30
Purchase #4	$61.73	7.731%	$66.5023	$66.50	$66.50	$66.50
Purchase #5	$29.58	5.586%	$31.2323	$31.23	$31.25	$31.20
Purchase #6	$87.45	12.862%	$98.6978	$98.70	$98.70	$98.70
Purchase #7	$127.31	4.568%	$133.1255	$133.13	$133.15	$133.10
7 purchase totals =	$507.50		$546.8143	$546.81	$546.85	$546.80