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	$76.46	9.115%	$83.4293	$83.43	$83.45	$83.40
Purchase #2	$133.53	12.152%	$149.7566	$149.76	$149.75	$149.80
Purchase #3	$202.51	13.806%	$230.4685	$230.47	$230.45	$230.50
Purchase #4	$42.67	8.718%	$46.39	$46.39	$46.40	$46.40
Purchase #5	$83.67	6.570%	$89.1671	$89.17	$89.15	$89.20
Purchase #6	$163.92	13.253%	$185.6443	$185.64	$185.65	$185.60
Purchase #7	$248.37	13.254%	$281.289	$281.29	$281.30	$281.30
7 purchase totals =	$951.13		$1,066.1448	$1,066.15	$1,066.15	$1,066.20