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	$137.39	7.853%	$148.1792	$148.18	$148.20	$148.20
Purchase #2	$45.55	10.714%	$50.4302	$50.43	$50.45	$50.40
Purchase #3	$147.99	5.292%	$155.8216	$155.82	$155.80	$155.80
Purchase #4	$211.43	10.832%	$234.3321	$234.33	$234.35	$234.30
Purchase #5	$17.25	13.596%	$19.5953	$19.60	$19.60	$19.60
Purchase #6	$166.47	10.569%	$184.0642	$184.06	$184.05	$184.10
Purchase #7	$164.68	4.732%	$172.4727	$172.47	$172.45	$172.50
7 purchase totals =	$890.76		$964.8953	$964.89	$964.90	$964.90