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	$192.31	6.339%	$204.5005	$204.50	$204.50	$204.50
Purchase #2	$126.60	4.634%	$132.4666	$132.47	$132.45	$132.50
Purchase #3	$235.60	5.338%	$248.1763	$248.18	$248.20	$248.20
Purchase #4	$84.30	5.735%	$89.1346	$89.13	$89.15	$89.10
Purchase #5	$53.33	12.105%	$59.7856	$59.79	$59.80	$59.80
Purchase #6	$85.51	5.577%	$90.2789	$90.28	$90.30	$90.30
Purchase #7	$8.27	10.812%	$9.1642	$9.16	$9.15	$9.20
7 purchase totals =	$785.92		$833.5067	$833.51	$833.55	$833.60