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	$143.46	11.852%	$160.4629	$160.46	$160.45	$160.50
Purchase #2	$46.52	8.189%	$50.3295	$50.33	$50.35	$50.30
Purchase #3	$247.53	8.157%	$267.721	$267.72	$267.70	$267.70
Purchase #4	$100.40	8.772%	$109.2071	$109.21	$109.20	$109.20
Purchase #5	$86.42	4.260%	$90.1015	$90.10	$90.10	$90.10
Purchase #6	$40.76	7.287%	$43.7302	$43.73	$43.75	$43.70
Purchase #7	$209.83	12.252%	$235.5384	$235.54	$235.55	$235.50
7 purchase totals =	$874.92		$957.0906	$957.09	$957.10	$957.00