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	$69.90	11.823%	$78.1643	$78.16	$78.15	$78.20
Purchase #2	$192.40	10.511%	$212.6232	$212.62	$212.60	$212.60
Purchase #3	$181.25	13.818%	$206.2951	$206.30	$206.30	$206.30
Purchase #4	$11.81	4.695%	$12.3645	$12.36	$12.35	$12.40
Purchase #5	$127.55	10.143%	$140.4874	$140.49	$140.50	$140.50
Purchase #6	$63.30	13.849%	$72.0664	$72.07	$72.05	$72.10
Purchase #7	$145.58	11.379%	$162.1455	$162.15	$162.15	$162.10
7 purchase totals =	$791.79		$884.1464	$884.15	$884.10	$884.20