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	$224.74	11.601%	$250.8121	$250.81	$250.80	$250.80
Purchase #2	$92.29	3.238%	$95.2784	$95.28	$95.30	$95.30
Purchase #3	$94.40	9.509%	$103.3765	$103.38	$103.40	$103.40
Purchase #4	$86.26	10.737%	$95.5217	$95.52	$95.50	$95.50
Purchase #5	$5.75	10.805%	$6.3713	$6.37	$6.35	$6.40
Purchase #6	$137.85	4.372%	$143.8768	$143.88	$143.90	$143.90
Purchase #7	$152.85	3.730%	$158.5513	$158.55	$158.55	$158.60
7 purchase totals =	$794.14		$853.7881	$853.79	$853.80	$853.90