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	$28.75	10.733%	$31.8357	$31.84	$31.85	$31.80
Purchase #2	$132.52	3.296%	$136.8879	$136.89	$136.90	$136.90
Purchase #3	$67.78	7.137%	$72.6175	$72.62	$72.60	$72.60
Purchase #4	$208.27	10.512%	$230.1633	$230.16	$230.15	$230.20
Purchase #5	$137.98	3.109%	$142.2698	$142.27	$142.25	$142.30
Purchase #6	$78.72	6.592%	$83.9092	$83.91	$83.90	$83.90
Purchase #7	$142.37	5.499%	$150.1989	$150.20	$150.20	$150.20
7 purchase totals =	$796.39		$847.8823	$847.89	$847.85	$847.90