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	$53.57	5.324%	$56.4221	$56.42	$56.40	$56.40
Purchase #2	$231.38	9.781%	$254.0113	$254.01	$254.00	$254.00
Purchase #3	$141.29	9.425%	$154.6066	$154.61	$154.60	$154.60
Purchase #4	$44.46	10.175%	$48.9838	$48.98	$49.00	$49.00
Purchase #5	$14.59	6.226%	$15.4984	$15.50	$15.50	$15.50
Purchase #6	$57.43	3.767%	$59.5934	$59.59	$59.60	$59.60
Purchase #7	$26.37	11.185%	$29.3195	$29.32	$29.30	$29.30
7 purchase totals =	$569.09		$618.4351	$618.43	$618.40	$618.40