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	$6.97	9.563%	$7.6365	$7.64	$7.65	$7.60
Purchase #2	$104.38	6.697%	$111.3703	$111.37	$111.35	$111.40
Purchase #3	$142.66	13.636%	$162.1131	$162.11	$162.10	$162.10
Purchase #4	$111.77	5.703%	$118.1442	$118.14	$118.15	$118.10
Purchase #5	$131.97	10.254%	$145.5022	$145.50	$145.50	$145.50
Purchase #6	$16.95	9.695%	$18.5933	$18.59	$18.60	$18.60
Purchase #7	$42.63	3.788%	$44.2448	$44.24	$44.25	$44.20
7 purchase totals =	$557.33		$607.6044	$607.59	$607.60	$607.50