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	$49.39	3.763%	$51.2485	$51.25	$51.25	$51.20
Purchase #2	$104.40	6.472%	$111.1568	$111.16	$111.15	$111.20
Purchase #3	$105.54	5.803%	$111.6645	$111.66	$111.65	$111.70
Purchase #4	$122.96	13.796%	$139.9236	$139.92	$139.90	$139.90
Purchase #5	$14.28	10.621%	$15.7967	$15.80	$15.80	$15.80
Purchase #6	$96.86	9.602%	$106.1605	$106.16	$106.15	$106.20
Purchase #7	$120.35	13.269%	$136.3192	$136.32	$136.30	$136.30
7 purchase totals =	$613.78		$672.2698	$672.27	$672.20	$672.30