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	$103.72	7.220%	$111.2086	$111.21	$111.20	$111.20
Purchase #2	$98.84	12.743%	$111.4352	$111.44	$111.45	$111.40
Purchase #3	$194.67	3.444%	$201.3744	$201.37	$201.35	$201.40
Purchase #4	$55.80	11.229%	$62.0658	$62.07	$62.05	$62.10
Purchase #5	$135.44	8.239%	$146.5989	$146.60	$146.60	$146.60
Purchase #6	$93.51	6.292%	$99.3936	$99.39	$99.40	$99.40
Purchase #7	$60.47	9.708%	$66.3404	$66.34	$66.35	$66.30
7 purchase totals =	$742.45		$798.4169	$798.42	$798.40	$798.40