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	$235.66	11.733%	$263.31	$263.31	$263.30	$263.30
Purchase #2	$31.83	9.434%	$34.8328	$34.83	$34.85	$34.80
Purchase #3	$222.50	12.510%	$250.3348	$250.33	$250.35	$250.30
Purchase #4	$94.43	12.384%	$106.1242	$106.12	$106.10	$106.10
Purchase #5	$72.32	8.343%	$78.3537	$78.35	$78.35	$78.40
Purchase #6	$153.59	4.781%	$160.9331	$160.93	$160.95	$160.90
Purchase #7	$11.85	7.206%	$12.7039	$12.70	$12.70	$12.70
7 purchase totals =	$822.18		$906.5925	$906.57	$906.60	$906.50