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	$16.78	10.788%	$18.5902	$18.59	$18.60	$18.60
Purchase #2	$99.87	11.555%	$111.41	$111.41	$111.40	$111.40
Purchase #3	$217.86	3.664%	$225.8424	$225.84	$225.85	$225.80
Purchase #4	$203.99	10.450%	$225.307	$225.31	$225.30	$225.30
Purchase #5	$83.56	4.682%	$87.4723	$87.47	$87.45	$87.50
Purchase #6	$71.38	8.435%	$77.4009	$77.40	$77.40	$77.40
Purchase #7	$171.83	6.682%	$183.3117	$183.31	$183.30	$183.30
7 purchase totals =	$865.27		$929.3345	$929.33	$929.30	$929.30