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	$109.98	7.682%	$118.4287	$118.43	$118.45	$118.40
Purchase #2	$107.66	6.239%	$114.3769	$114.38	$114.40	$114.40
Purchase #3	$214.25	11.394%	$238.6616	$238.66	$238.65	$238.70
Purchase #4	$96.82	6.177%	$102.8006	$102.80	$102.80	$102.80
Purchase #5	$25.84	6.324%	$27.4741	$27.47	$27.45	$27.50
Purchase #6	$100.54	11.256%	$111.8568	$111.86	$111.85	$111.90
Purchase #7	$54.55	11.770%	$60.9705	$60.97	$60.95	$61.00
7 purchase totals =	$709.64		$774.5692	$774.57	$774.55	$774.70