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	$173.40	6.647%	$184.9259	$184.93	$184.95	$184.90
Purchase #2	$153.71	4.475%	$160.5885	$160.59	$160.60	$160.60
Purchase #3	$172.47	10.561%	$190.6846	$190.68	$190.70	$190.70
Purchase #4	$59.47	12.284%	$66.7753	$66.78	$66.80	$66.80
Purchase #5	$148.31	9.787%	$162.8251	$162.83	$162.85	$162.80
Purchase #6	$160.73	6.295%	$170.848	$170.85	$170.85	$170.80
Purchase #7	$18.88	13.824%	$21.49	$21.49	$21.50	$21.50
7 purchase totals =	$886.97		$958.1374	$958.15	$958.25	$958.10