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	$148.81	4.487%	$155.4871	$155.49	$155.50	$155.50
Purchase #2	$67.35	8.207%	$72.8774	$72.88	$72.90	$72.90
Purchase #3	$135.84	6.863%	$145.1627	$145.16	$145.15	$145.20
Purchase #4	$158.66	4.310%	$165.4982	$165.50	$165.50	$165.50
Purchase #5	$11.35	11.209%	$12.6222	$12.62	$12.60	$12.60
Purchase #6	$40.50	7.654%	$43.5999	$43.60	$43.60	$43.60
Purchase #7	$56.84	9.105%	$62.0153	$62.02	$62.00	$62.00
7 purchase totals =	$619.35		$657.2628	$657.27	$657.25	$657.30