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	$100.29	9.467%	$109.7845	$109.78	$109.80	$109.80
Purchase #2	$188.70	10.770%	$209.023	$209.02	$209.00	$209.00
Purchase #3	$21.63	10.261%	$23.8495	$23.85	$23.85	$23.80
Purchase #4	$98.82	4.105%	$102.8766	$102.88	$102.90	$102.90
Purchase #5	$161.56	12.652%	$182.0006	$182.00	$182.00	$182.00
Purchase #6	$153.93	3.213%	$158.8758	$158.88	$158.90	$158.90
Purchase #7	$180.34	13.731%	$205.1025	$205.10	$205.10	$205.10
7 purchase totals =	$905.27		$991.5125	$991.51	$991.55	$991.50