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	$11.28	6.151%	$11.9738	$11.97	$11.95	$12.00
Purchase #2	$38.47	3.721%	$39.9015	$39.90	$39.90	$39.90
Purchase #3	$54.77	4.176%	$57.0572	$57.06	$57.05	$57.10
Purchase #4	$13.52	9.332%	$14.7817	$14.78	$14.80	$14.80
Purchase #5	$181.70	4.855%	$190.5215	$190.52	$190.50	$190.50
Purchase #6	$52.41	5.684%	$55.389	$55.39	$55.40	$55.40
Purchase #7	$232.95	3.554%	$241.229	$241.23	$241.25	$241.20
7 purchase totals =	$585.10		$610.8537	$610.85	$610.85	$610.90