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	$82.82	9.528%	$90.7111	$90.71	$90.70	$90.70
Purchase #2	$102.50	13.417%	$116.2524	$116.25	$116.25	$116.30
Purchase #3	$148.60	11.722%	$166.0189	$166.02	$166.00	$166.00
Purchase #4	$61.52	11.763%	$68.7566	$68.76	$68.75	$68.80
Purchase #5	$192.57	11.788%	$215.2702	$215.27	$215.25	$215.30
Purchase #6	$67.96	4.366%	$70.9271	$70.93	$70.95	$70.90
Purchase #7	$230.38	4.871%	$241.6018	$241.60	$241.60	$241.60
7 purchase totals =	$886.35		$969.5381	$969.54	$969.50	$969.60