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	$130.81	11.482%	$145.8296	$145.83	$145.85	$145.80
Purchase #2	$114.99	7.321%	$123.4084	$123.41	$123.40	$123.40
Purchase #3	$169.47	12.858%	$191.2605	$191.26	$191.25	$191.30
Purchase #4	$10.68	12.788%	$12.0458	$12.05	$12.05	$12.00
Purchase #5	$51.66	10.765%	$57.2212	$57.22	$57.20	$57.20
Purchase #6	$127.62	3.661%	$132.2922	$132.29	$132.30	$132.30
Purchase #7	$160.59	4.672%	$168.0928	$168.09	$168.10	$168.10
7 purchase totals =	$765.82		$830.1505	$830.15	$830.15	$830.10