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	$134.52	4.730%	$140.8828	$140.88	$140.90	$140.90
Purchase #2	$213.47	11.854%	$238.7747	$238.77	$238.75	$238.80
Purchase #3	$173.39	7.785%	$186.8884	$186.89	$186.90	$186.90
Purchase #4	$48.32	12.365%	$54.2948	$54.29	$54.30	$54.30
Purchase #5	$61.66	13.748%	$70.137	$70.14	$70.15	$70.10
Purchase #6	$138.86	4.333%	$144.8768	$144.88	$144.90	$144.90
Purchase #7	$51.68	6.348%	$54.9606	$54.96	$54.95	$55.00
7 purchase totals =	$821.90		$890.8151	$890.81	$890.85	$890.90