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	$206.45	11.493%	$230.1773	$230.18	$230.20	$230.20
Purchase #2	$19.31	6.580%	$20.5806	$20.58	$20.60	$20.60
Purchase #3	$126.70	3.284%	$130.8608	$130.86	$130.85	$130.90
Purchase #4	$238.36	8.301%	$258.1463	$258.15	$258.15	$258.10
Purchase #5	$92.93	8.511%	$100.8393	$100.84	$100.85	$100.80
Purchase #6	$117.54	12.601%	$132.3512	$132.35	$132.35	$132.40
Purchase #7	$95.54	4.542%	$99.8794	$99.88	$99.90	$99.90
7 purchase totals =	$896.83		$972.8349	$972.84	$972.90	$972.90