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	$94.76	8.671%	$102.9766	$102.98	$103.00	$103.00
Purchase #2	$151.81	4.584%	$158.769	$158.77	$158.75	$158.80
Purchase #3	$11.88	7.773%	$12.8034	$12.80	$12.80	$12.80
Purchase #4	$172.39	8.279%	$186.6622	$186.66	$186.65	$186.70
Purchase #5	$51.48	6.231%	$54.6877	$54.69	$54.70	$54.70
Purchase #6	$250.79	13.183%	$283.8516	$283.85	$283.85	$283.90
Purchase #7	$236.83	7.862%	$255.4496	$255.45	$255.45	$255.40
7 purchase totals =	$969.94		$1,055.2001	$1,055.20	$1,055.20	$1,055.30