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	$138.81	12.367%	$155.9766	$155.98	$156.00	$156.00
Purchase #2	$48.84	11.536%	$54.4742	$54.47	$54.45	$54.50
Purchase #3	$57.30	12.397%	$64.4035	$64.40	$64.40	$64.40
Purchase #4	$90.39	10.318%	$99.7164	$99.72	$99.70	$99.70
Purchase #5	$166.72	5.844%	$176.4631	$176.46	$176.45	$176.50
Purchase #6	$36.81	11.694%	$41.1146	$41.11	$41.10	$41.10
Purchase #7	$179.97	6.836%	$192.2727	$192.27	$192.25	$192.30
7 purchase totals =	$718.84		$784.4211	$784.41	$784.35	$784.50