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	$24.53	13.741%	$27.9007	$27.90	$27.90	$27.90
Purchase #2	$164.26	6.781%	$175.3985	$175.40	$175.40	$175.40
Purchase #3	$193.37	13.559%	$219.589	$219.59	$219.60	$219.60
Purchase #4	$180.68	10.768%	$200.1356	$200.14	$200.15	$200.10
Purchase #5	$47.91	7.318%	$51.4161	$51.42	$51.40	$51.40
Purchase #6	$173.81	6.704%	$185.4622	$185.46	$185.45	$185.50
Purchase #7	$48.47	4.133%	$50.4733	$50.47	$50.45	$50.50
7 purchase totals =	$833.03		$910.3754	$910.38	$910.35	$910.40