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	$27.90	13.226%	$31.5901	$31.59	$31.60	$31.60
Purchase #2	$150.82	13.723%	$171.517	$171.52	$171.50	$171.50
Purchase #3	$135.33	8.513%	$146.8506	$146.85	$146.85	$146.90
Purchase #4	$119.70	5.494%	$126.2763	$126.28	$126.30	$126.30
Purchase #5	$37.44	5.275%	$39.415	$39.42	$39.40	$39.40
Purchase #6	$241.25	6.156%	$256.1014	$256.10	$256.10	$256.10
Purchase #7	$164.65	12.326%	$184.9448	$184.94	$184.95	$184.90
7 purchase totals =	$877.09		$956.6952	$956.70	$956.70	$956.70