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	$185.88	8.598%	$201.862	$201.86	$201.85	$201.90
Purchase #2	$131.29	9.698%	$144.0225	$144.02	$144.00	$144.00
Purchase #3	$114.59	10.407%	$126.5154	$126.52	$126.50	$126.50
Purchase #4	$182.82	12.303%	$205.3123	$205.31	$205.30	$205.30
Purchase #5	$63.85	12.499%	$71.8306	$71.83	$71.85	$71.80
Purchase #6	$16.59	12.732%	$18.7022	$18.70	$18.70	$18.70
Purchase #7	$158.64	4.394%	$165.6106	$165.61	$165.60	$165.60
7 purchase totals =	$853.66		$933.8556	$933.85	$933.80	$933.80