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	$20.58	3.590%	$21.3188	$21.32	$21.30	$21.30
Purchase #2	$100.58	10.533%	$111.1741	$111.17	$111.15	$111.20
Purchase #3	$13.42	12.822%	$15.1407	$15.14	$15.15	$15.10
Purchase #4	$120.97	10.298%	$133.4275	$133.43	$133.45	$133.40
Purchase #5	$156.57	11.246%	$174.1779	$174.18	$174.20	$174.20
Purchase #6	$100.85	6.703%	$107.61	$107.61	$107.60	$107.60
Purchase #7	$245.61	10.138%	$270.5099	$270.51	$270.50	$270.50
7 purchase totals =	$758.58		$833.3589	$833.36	$833.35	$833.30