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	$89.99	12.643%	$101.3674	$101.37	$101.35	$101.40
Purchase #2	$105.64	9.270%	$115.4328	$115.43	$115.45	$115.40
Purchase #3	$248.51	8.801%	$270.3814	$270.38	$270.40	$270.40
Purchase #4	$48.85	3.174%	$50.4005	$50.40	$50.40	$50.40
Purchase #5	$94.31	5.445%	$99.4452	$99.45	$99.45	$99.40
Purchase #6	$126.78	8.252%	$137.2419	$137.24	$137.25	$137.20
Purchase #7	$54.30	10.104%	$59.7865	$59.79	$59.80	$59.80
7 purchase totals =	$768.38		$834.0557	$834.06	$834.10	$834.00