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	$59.82	11.151%	$66.4905	$66.49	$66.50	$66.50
Purchase #2	$39.86	13.379%	$45.1929	$45.19	$45.20	$45.20
Purchase #3	$136.95	3.850%	$142.2226	$142.22	$142.20	$142.20
Purchase #4	$39.58	8.689%	$43.0191	$43.02	$43.00	$43.00
Purchase #5	$162.76	6.633%	$173.5559	$173.56	$173.55	$173.60
Purchase #6	$86.35	10.507%	$95.4228	$95.42	$95.40	$95.40
Purchase #7	$23.31	10.297%	$25.7102	$25.71	$25.70	$25.70
7 purchase totals =	$548.63		$591.6140	$591.61	$591.55	$591.60