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	$146.62	6.742%	$156.5051	$156.51	$156.50	$156.50
Purchase #2	$138.82	10.377%	$153.2254	$153.23	$153.25	$153.20
Purchase #3	$71.80	8.733%	$78.0703	$78.07	$78.05	$78.10
Purchase #4	$47.55	7.721%	$51.2213	$51.22	$51.20	$51.20
Purchase #5	$128.84	11.580%	$143.7597	$143.76	$143.75	$143.80
Purchase #6	$80.95	13.543%	$91.9131	$91.91	$91.90	$91.90
Purchase #7	$65.68	9.555%	$71.9557	$71.96	$71.95	$72.00
7 purchase totals =	$680.26		$746.6506	$746.66	$746.60	$746.70