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	$192.51	6.701%	$205.4101	$205.41	$205.40	$205.40
Purchase #2	$160.49	7.570%	$172.6391	$172.64	$172.65	$172.60
Purchase #3	$180.60	13.663%	$205.2754	$205.28	$205.30	$205.30
Purchase #4	$29.38	4.482%	$30.6968	$30.70	$30.70	$30.70
Purchase #5	$97.32	6.865%	$104.001	$104.00	$104.00	$104.00
Purchase #6	$27.92	12.853%	$31.5086	$31.51	$31.50	$31.50
Purchase #7	$215.81	6.250%	$229.2981	$229.30	$229.30	$229.30
7 purchase totals =	$904.03		$978.8291	$978.84	$978.85	$978.80