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	$120.70	13.414%	$136.8907	$136.89	$136.90	$136.90
Purchase #2	$21.83	6.396%	$23.2262	$23.23	$23.25	$23.20
Purchase #3	$175.72	5.516%	$185.4127	$185.41	$185.40	$185.40
Purchase #4	$117.46	13.160%	$132.9177	$132.92	$132.90	$132.90
Purchase #5	$40.86	4.737%	$42.7955	$42.80	$42.80	$42.80
Purchase #6	$22.76	7.353%	$24.4335	$24.43	$24.45	$24.40
Purchase #7	$155.75	10.728%	$172.4589	$172.46	$172.45	$172.50
7 purchase totals =	$655.08		$718.1352	$718.14	$718.15	$718.10