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	$143.27	10.389%	$158.1543	$158.15	$158.15	$158.20
Purchase #2	$36.92	3.425%	$38.1845	$38.18	$38.20	$38.20
Purchase #3	$155.35	3.317%	$160.503	$160.50	$160.50	$160.50
Purchase #4	$94.81	12.113%	$106.2943	$106.29	$106.30	$106.30
Purchase #5	$127.84	11.465%	$142.4969	$142.50	$142.50	$142.50
Purchase #6	$78.52	11.836%	$87.8136	$87.81	$87.80	$87.80
Purchase #7	$62.41	4.373%	$65.1392	$65.14	$65.15	$65.10
7 purchase totals =	$699.12		$758.5858	$758.57	$758.60	$758.60