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	$9.59	10.799%	$10.6256	$10.63	$10.65	$10.60
Purchase #2	$138.61	4.813%	$145.2813	$145.28	$145.30	$145.30
Purchase #3	$103.58	9.450%	$113.3683	$113.37	$113.35	$113.40
Purchase #4	$100.70	10.243%	$111.0147	$111.01	$111.00	$111.00
Purchase #5	$166.36	9.364%	$181.938	$181.94	$181.95	$181.90
Purchase #6	$172.88	12.312%	$194.165	$194.17	$194.15	$194.20
Purchase #7	$248.83	13.268%	$281.8448	$281.84	$281.85	$281.80
7 purchase totals =	$940.55		$1,038.2377	$1,038.24	$1,038.25	$1,038.20