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	$45.58	4.398%	$47.5846	$47.58	$47.60	$47.60
Purchase #2	$110.92	11.542%	$123.7224	$123.72	$123.70	$123.70
Purchase #3	$98.83	10.694%	$109.3989	$109.40	$109.40	$109.40
Purchase #4	$151.38	8.378%	$164.0626	$164.06	$164.05	$164.10
Purchase #5	$177.67	12.870%	$200.5361	$200.54	$200.55	$200.50
Purchase #6	$151.47	7.648%	$163.0544	$163.05	$163.05	$163.10
Purchase #7	$166.38	8.847%	$181.0996	$181.10	$181.10	$181.10
7 purchase totals =	$902.23		$989.4586	$989.45	$989.45	$989.50