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	$107.74	7.867%	$116.2159	$116.22	$116.20	$116.20
Purchase #2	$144.82	8.311%	$156.856	$156.86	$156.85	$156.90
Purchase #3	$187.25	7.149%	$200.6365	$200.64	$200.65	$200.60
Purchase #4	$184.51	3.196%	$190.4069	$190.41	$190.40	$190.40
Purchase #5	$234.88	13.251%	$266.0039	$266.00	$266.00	$266.00
Purchase #6	$202.82	9.714%	$222.5219	$222.52	$222.50	$222.50
Purchase #7	$104.67	13.394%	$118.6895	$118.69	$118.70	$118.70
7 purchase totals =	$1,166.69		$1,271.3306	$1,271.34	$1,271.30	$1,271.30