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	$93.84	7.142%	$100.5421	$100.54	$100.55	$100.50
Purchase #2	$90.80	11.126%	$100.9024	$100.90	$100.90	$100.90
Purchase #3	$52.45	3.701%	$54.3912	$54.39	$54.40	$54.40
Purchase #4	$84.44	4.725%	$88.4298	$88.43	$88.45	$88.40
Purchase #5	$90.30	4.105%	$94.0068	$94.01	$94.00	$94.00
Purchase #6	$222.66	7.384%	$239.1012	$239.10	$239.10	$239.10
Purchase #7	$146.42	8.242%	$158.4879	$158.49	$158.50	$158.50
7 purchase totals =	$780.91		$835.8614	$835.86	$835.90	$835.80