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	$81.45	9.865%	$89.485	$89.49	$89.50	$89.50
Purchase #2	$55.32	10.605%	$61.1867	$61.19	$61.20	$61.20
Purchase #3	$63.80	11.123%	$70.8965	$70.90	$70.90	$70.90
Purchase #4	$56.39	13.447%	$63.9728	$63.97	$63.95	$64.00
Purchase #5	$42.82	10.652%	$47.3812	$47.38	$47.40	$47.40
Purchase #6	$210.95	10.841%	$233.8191	$233.82	$233.80	$233.80
Purchase #7	$154.94	13.325%	$175.5858	$175.59	$175.60	$175.60
7 purchase totals =	$665.67		$742.3271	$742.34	$742.35	$742.40