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	$11.26	10.736%	$12.4689	$12.47	$12.45	$12.50
Purchase #2	$154.58	6.783%	$165.0652	$165.07	$165.05	$165.10
Purchase #3	$137.58	5.526%	$145.1827	$145.18	$145.20	$145.20
Purchase #4	$30.91	13.450%	$35.0674	$35.07	$35.05	$35.10
Purchase #5	$244.30	4.840%	$256.1241	$256.12	$256.10	$256.10
Purchase #6	$19.81	6.824%	$21.1618	$21.16	$21.15	$21.20
Purchase #7	$118.32	7.698%	$127.4283	$127.43	$127.45	$127.40
7 purchase totals =	$716.76		$762.4984	$762.50	$762.45	$762.60