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	$66.71	5.690%	$70.5058	$70.51	$70.50	$70.50
Purchase #2	$225.92	3.482%	$233.7865	$233.79	$233.80	$233.80
Purchase #3	$33.60	11.636%	$37.5097	$37.51	$37.50	$37.50
Purchase #4	$40.99	12.338%	$46.0473	$46.05	$46.05	$46.00
Purchase #5	$17.91	4.371%	$18.6928	$18.69	$18.70	$18.70
Purchase #6	$83.30	8.376%	$90.2772	$90.28	$90.30	$90.30
Purchase #7	$73.97	12.286%	$83.058	$83.06	$83.05	$83.10
7 purchase totals =	$542.40		$579.8773	$579.89	$579.90	$579.90