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	$234.70	10.533%	$259.421	$259.42	$259.40	$259.40
Purchase #2	$78.69	13.279%	$89.1392	$89.14	$89.15	$89.10
Purchase #3	$137.55	4.425%	$143.6366	$143.64	$143.65	$143.60
Purchase #4	$41.33	13.752%	$47.0137	$47.01	$47.00	$47.00
Purchase #5	$233.31	3.530%	$241.5458	$241.55	$241.55	$241.50
Purchase #6	$62.25	13.795%	$70.8374	$70.84	$70.85	$70.80
Purchase #7	$52.49	5.874%	$55.5733	$55.57	$55.55	$55.60
7 purchase totals =	$840.32		$907.1670	$907.17	$907.15	$907.00