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	$94.96	6.156%	$100.8057	$100.81	$100.80	$100.80
Purchase #2	$140.93	3.790%	$146.2712	$146.27	$146.25	$146.30
Purchase #3	$11.78	9.545%	$12.9044	$12.90	$12.90	$12.90
Purchase #4	$127.37	5.795%	$134.7511	$134.75	$134.75	$134.80
Purchase #5	$12.56	9.827%	$13.7943	$13.79	$13.80	$13.80
Purchase #6	$207.45	7.128%	$222.237	$222.24	$222.25	$222.20
Purchase #7	$44.28	4.779%	$46.3961	$46.40	$46.40	$46.40
7 purchase totals =	$639.33		$677.1598	$677.16	$677.15	$677.20