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	$105.70	5.715%	$111.7408	$111.74	$111.75	$111.70
Purchase #2	$153.99	4.254%	$160.5407	$160.54	$160.55	$160.50
Purchase #3	$120.72	3.278%	$124.6772	$124.68	$124.70	$124.70
Purchase #4	$209.99	8.868%	$228.6119	$228.61	$228.60	$228.60
Purchase #5	$85.83	9.836%	$94.2722	$94.27	$94.25	$94.30
Purchase #6	$146.51	12.333%	$164.5791	$164.58	$164.60	$164.60
Purchase #7	$83.91	7.262%	$90.0035	$90.00	$90.00	$90.00
7 purchase totals =	$906.65		$974.4254	$974.42	$974.45	$974.40