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	$161.68	13.557%	$183.599	$183.60	$183.60	$183.60
Purchase #2	$6.80	11.698%	$7.5955	$7.60	$7.60	$7.60
Purchase #3	$131.42	11.300%	$146.2705	$146.27	$146.25	$146.30
Purchase #4	$149.35	10.260%	$164.6733	$164.67	$164.65	$164.70
Purchase #5	$166.47	11.555%	$185.7056	$185.71	$185.70	$185.70
Purchase #6	$13.59	6.674%	$14.497	$14.50	$14.50	$14.50
Purchase #7	$132.59	4.546%	$138.6175	$138.62	$138.60	$138.60
7 purchase totals =	$761.90		$840.9584	$840.97	$840.90	$841.00