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	$180.30	6.870%	$192.6866	$192.69	$192.70	$192.70
Purchase #2	$55.38	12.774%	$62.4542	$62.45	$62.45	$62.50
Purchase #3	$158.84	3.790%	$164.86	$164.86	$164.85	$164.90
Purchase #4	$118.46	11.580%	$132.1777	$132.18	$132.20	$132.20
Purchase #5	$9.97	9.316%	$10.8988	$10.90	$10.90	$10.90
Purchase #6	$103.60	8.126%	$112.0185	$112.02	$112.00	$112.00
Purchase #7	$233.85	13.470%	$265.3496	$265.35	$265.35	$265.30
7 purchase totals =	$860.40		$940.4454	$940.45	$940.45	$940.50