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	$93.88	10.574%	$103.8069	$103.81	$103.80	$103.80
Purchase #2	$66.28	9.210%	$72.3844	$72.38	$72.40	$72.40
Purchase #3	$180.41	10.199%	$198.81	$198.81	$198.80	$198.80
Purchase #4	$29.56	11.195%	$32.8692	$32.87	$32.85	$32.90
Purchase #5	$139.28	12.279%	$156.3822	$156.38	$156.40	$156.40
Purchase #6	$111.43	6.852%	$119.0652	$119.07	$119.05	$119.10
Purchase #7	$201.78	6.785%	$215.4708	$215.47	$215.45	$215.50
7 purchase totals =	$822.62		$898.7887	$898.79	$898.75	$898.90