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	$170.59	4.593%	$178.4252	$178.43	$178.45	$178.40
Purchase #2	$136.96	3.665%	$141.9796	$141.98	$142.00	$142.00
Purchase #3	$184.62	3.203%	$190.5334	$190.53	$190.55	$190.50
Purchase #4	$71.72	7.672%	$77.2224	$77.22	$77.20	$77.20
Purchase #5	$48.46	6.345%	$51.5348	$51.53	$51.55	$51.50
Purchase #6	$120.31	10.441%	$132.8716	$132.87	$132.85	$132.90
Purchase #7	$9.37	10.154%	$10.3214	$10.32	$10.30	$10.30
7 purchase totals =	$742.03		$782.8884	$782.88	$782.90	$782.80