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	$137.76	13.575%	$156.4609	$156.46	$156.45	$156.50
Purchase #2	$198.73	3.464%	$205.614	$205.61	$205.60	$205.60
Purchase #3	$16.47	12.540%	$18.5353	$18.54	$18.55	$18.50
Purchase #4	$95.95	4.860%	$100.6132	$100.61	$100.60	$100.60
Purchase #5	$186.88	3.118%	$192.7069	$192.71	$192.70	$192.70
Purchase #6	$21.80	6.611%	$23.2412	$23.24	$23.25	$23.20
Purchase #7	$54.59	8.626%	$59.2989	$59.30	$59.30	$59.30
7 purchase totals =	$712.18		$756.4704	$756.47	$756.45	$756.40