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	$206.38	8.286%	$223.4806	$223.48	$223.50	$223.50
Purchase #2	$12.58	4.711%	$13.1726	$13.17	$13.15	$13.20
Purchase #3	$219.37	5.255%	$230.8979	$230.90	$230.90	$230.90
Purchase #4	$19.61	10.141%	$21.5987	$21.60	$21.60	$21.60
Purchase #5	$160.54	4.851%	$168.3278	$168.33	$168.35	$168.30
Purchase #6	$191.85	8.705%	$208.5505	$208.55	$208.55	$208.60
Purchase #7	$106.79	6.819%	$114.072	$114.07	$114.05	$114.10
7 purchase totals =	$917.12		$980.1001	$980.10	$980.10	$980.20