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	$151.93	9.302%	$166.0625	$166.06	$166.05	$166.10
Purchase #2	$211.86	4.866%	$222.1691	$222.17	$222.15	$222.20
Purchase #3	$35.96	11.833%	$40.2151	$40.22	$40.20	$40.20
Purchase #4	$44.67	4.803%	$46.8155	$46.82	$46.80	$46.80
Purchase #5	$246.90	13.510%	$280.2562	$280.26	$280.25	$280.30
Purchase #6	$152.74	13.493%	$173.3492	$173.35	$173.35	$173.30
Purchase #7	$47.92	10.185%	$52.8007	$52.80	$52.80	$52.80
7 purchase totals =	$891.98		$981.6683	$981.68	$981.60	$981.70