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	$245.89	3.626%	$254.806	$254.81	$254.80	$254.80
Purchase #2	$208.82	9.404%	$228.4574	$228.46	$228.45	$228.50
Purchase #3	$184.86	10.257%	$203.8211	$203.82	$203.80	$203.80
Purchase #4	$230.32	4.536%	$240.7673	$240.77	$240.75	$240.80
Purchase #5	$52.38	7.242%	$56.1734	$56.17	$56.15	$56.20
Purchase #6	$81.84	3.613%	$84.7969	$84.80	$84.80	$84.80
Purchase #7	$39.25	9.157%	$42.8441	$42.84	$42.85	$42.80
7 purchase totals =	$1,043.36		$1,111.6662	$1,111.67	$1,111.60	$1,111.70