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	$250.66	9.686%	$274.9389	$274.94	$274.95	$274.90
Purchase #2	$131.59	5.758%	$139.167	$139.17	$139.15	$139.20
Purchase #3	$145.59	3.317%	$150.4192	$150.42	$150.40	$150.40
Purchase #4	$87.74	4.433%	$91.6295	$91.63	$91.65	$91.60
Purchase #5	$245.86	3.699%	$254.9544	$254.95	$254.95	$255.00
Purchase #6	$18.85	12.177%	$21.1454	$21.15	$21.15	$21.10
Purchase #7	$235.95	5.358%	$248.5922	$248.59	$248.60	$248.60
7 purchase totals =	$1,116.24		$1,180.8466	$1,180.85	$1,180.85	$1,180.80