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	$83.97	8.118%	$90.7867	$90.79	$90.80	$90.80
Purchase #2	$157.90	5.448%	$166.5024	$166.50	$166.50	$166.50
Purchase #3	$140.62	4.480%	$146.9198	$146.92	$146.90	$146.90
Purchase #4	$140.81	13.637%	$160.0123	$160.01	$160.00	$160.00
Purchase #5	$147.84	7.409%	$158.7935	$158.79	$158.80	$158.80
Purchase #6	$90.92	10.476%	$100.4448	$100.44	$100.45	$100.40
Purchase #7	$15.98	10.140%	$17.6004	$17.60	$17.60	$17.60
7 purchase totals =	$778.04		$841.0599	$841.05	$841.05	$841.00