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	$231.36	4.857%	$242.5972	$242.60	$242.60	$242.60
Purchase #2	$40.68	3.854%	$42.2478	$42.25	$42.25	$42.20
Purchase #3	$205.58	12.291%	$230.8478	$230.85	$230.85	$230.80
Purchase #4	$77.73	12.675%	$87.5823	$87.58	$87.60	$87.60
Purchase #5	$99.73	10.161%	$109.8636	$109.86	$109.85	$109.90
Purchase #6	$75.85	3.167%	$78.2522	$78.25	$78.25	$78.30
Purchase #7	$94.49	4.470%	$98.7137	$98.71	$98.70	$98.70
7 purchase totals =	$825.42		$890.1046	$890.10	$890.10	$890.10