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	$209.68	5.685%	$221.6003	$221.60	$221.60	$221.60
Purchase #2	$246.88	6.193%	$262.1693	$262.17	$262.15	$262.20
Purchase #3	$157.90	10.182%	$173.9774	$173.98	$174.00	$174.00
Purchase #4	$116.38	10.685%	$128.8152	$128.82	$128.80	$128.80
Purchase #5	$168.45	13.812%	$191.7163	$191.72	$191.70	$191.70
Purchase #6	$84.57	6.420%	$89.9994	$90.00	$90.00	$90.00
Purchase #7	$244.85	3.873%	$254.333	$254.33	$254.35	$254.30
7 purchase totals =	$1,228.71		$1,322.6109	$1,322.62	$1,322.60	$1,322.60