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	$33.90	12.314%	$38.0744	$38.07	$38.05	$38.10
Purchase #2	$144.60	12.369%	$162.4856	$162.49	$162.50	$162.50
Purchase #3	$40.77	6.615%	$43.4669	$43.47	$43.45	$43.50
Purchase #4	$161.55	13.278%	$183.0006	$183.00	$183.00	$183.00
Purchase #5	$198.83	5.415%	$209.5966	$209.60	$209.60	$209.60
Purchase #6	$89.77	11.482%	$100.0774	$100.08	$100.10	$100.10
Purchase #7	$12.39	6.256%	$13.1651	$13.17	$13.15	$13.20
7 purchase totals =	$681.81		$749.8666	$749.88	$749.85	$750.00