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	$140.28	3.223%	$144.8012	$144.80	$144.80	$144.80
Purchase #2	$183.31	9.457%	$200.6456	$200.65	$200.65	$200.60
Purchase #3	$224.58	6.295%	$238.7173	$238.72	$238.70	$238.70
Purchase #4	$116.78	12.803%	$131.7313	$131.73	$131.75	$131.70
Purchase #5	$143.49	10.374%	$158.3757	$158.38	$158.40	$158.40
Purchase #6	$142.93	13.770%	$162.6115	$162.61	$162.60	$162.60
Purchase #7	$240.70	7.414%	$258.5455	$258.55	$258.55	$258.50
7 purchase totals =	$1,192.07		$1,295.4281	$1,295.44	$1,295.45	$1,295.30