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	$246.97	4.273%	$257.523	$257.52	$257.50	$257.50
Purchase #2	$59.49	12.221%	$66.7603	$66.76	$66.75	$66.80
Purchase #3	$145.60	4.622%	$152.3296	$152.33	$152.35	$152.30
Purchase #4	$90.40	10.435%	$99.8332	$99.83	$99.85	$99.80
Purchase #5	$41.28	3.590%	$42.762	$42.76	$42.75	$42.80
Purchase #6	$183.79	12.665%	$207.067	$207.07	$207.05	$207.10
Purchase #7	$165.57	4.775%	$173.476	$173.48	$173.50	$173.50
7 purchase totals =	$933.10		$999.7511	$999.75	$999.75	$999.80