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	$126.76	3.846%	$131.6352	$131.64	$131.65	$131.60
Purchase #2	$36.29	12.815%	$40.9406	$40.94	$40.95	$40.90
Purchase #3	$85.58	12.446%	$96.2313	$96.23	$96.25	$96.20
Purchase #4	$205.64	5.296%	$216.5307	$216.53	$216.55	$216.50
Purchase #5	$227.91	6.527%	$242.7857	$242.79	$242.80	$242.80
Purchase #6	$179.55	4.627%	$187.8578	$187.86	$187.85	$187.90
Purchase #7	$49.83	8.553%	$54.092	$54.09	$54.10	$54.10
7 purchase totals =	$911.56		$970.0733	$970.08	$970.15	$970.00