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	$215.60	3.782%	$223.754	$223.75	$223.75	$223.80
Purchase #2	$109.82	12.466%	$123.5102	$123.51	$123.50	$123.50
Purchase #3	$132.86	9.590%	$145.6013	$145.60	$145.60	$145.60
Purchase #4	$56.43	4.825%	$59.1527	$59.15	$59.15	$59.20
Purchase #5	$82.58	8.667%	$89.7372	$89.74	$89.75	$89.70
Purchase #6	$241.48	8.492%	$261.9865	$261.99	$262.00	$262.00
Purchase #7	$230.79	10.189%	$254.3052	$254.31	$254.30	$254.30
7 purchase totals =	$1,069.56		$1,158.0471	$1,158.05	$1,158.05	$1,158.10