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	$135.39	6.618%	$144.3501	$144.35	$144.35	$144.40
Purchase #2	$64.40	5.849%	$68.1668	$68.17	$68.15	$68.20
Purchase #3	$158.38	9.315%	$173.1331	$173.13	$173.15	$173.10
Purchase #4	$225.29	9.816%	$247.4045	$247.40	$247.40	$247.40
Purchase #5	$103.74	7.261%	$111.2726	$111.27	$111.25	$111.30
Purchase #6	$34.27	8.221%	$37.0873	$37.09	$37.10	$37.10
Purchase #7	$117.42	5.582%	$123.9744	$123.97	$123.95	$124.00
7 purchase totals =	$838.89		$905.3888	$905.38	$905.35	$905.50