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	$97.97	13.685%	$111.3772	$111.38	$111.40	$111.40
Purchase #2	$230.80	8.406%	$250.201	$250.20	$250.20	$250.20
Purchase #3	$81.89	7.568%	$88.0874	$88.09	$88.10	$88.10
Purchase #4	$131.46	6.670%	$140.2284	$140.23	$140.25	$140.20
Purchase #5	$58.83	7.769%	$63.4005	$63.40	$63.40	$63.40
Purchase #6	$126.84	4.409%	$132.4324	$132.43	$132.45	$132.40
Purchase #7	$83.81	7.831%	$90.3732	$90.37	$90.35	$90.40
7 purchase totals =	$811.60		$876.1001	$876.10	$876.15	$876.10