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	$134.37	6.705%	$143.3795	$143.38	$143.40	$143.40
Purchase #2	$99.39	12.842%	$112.1537	$112.15	$112.15	$112.20
Purchase #3	$141.78	4.691%	$148.4309	$148.43	$148.45	$148.40
Purchase #4	$91.37	3.322%	$94.4053	$94.41	$94.40	$94.40
Purchase #5	$214.52	13.861%	$244.2546	$244.25	$244.25	$244.30
Purchase #6	$106.63	4.613%	$111.5488	$111.55	$111.55	$111.50
Purchase #7	$83.46	8.813%	$90.8153	$90.82	$90.80	$90.80
7 purchase totals =	$871.52		$944.9881	$944.99	$945.00	$945.00